Defensive realism and the Concert of Europe

Why do great powers expand? Offensive realist John Mearsheimer claims that states wage an eternal struggle for power, and that those strong enough to seek regional hegemony nearly always do. Mearsheimer’s evidence, however, displays a selection bias. Examining four crises between 1814 and 1840, I show that the balance of power restrained Russia, Prussia and France. Yet all three also exercised self-restraint; Russia, in particular, passed up chances to bid for hegemony in 1815 and to topple Ottoman Turkey in 1829. Defensive realism gives a better account of the Concert of Europe, because it combines structural realism with non-realist theories of state preferences.

Does every state that spots a chance for hegemony really make a run for it? Are the rest Nazi Germany wannabes, but too weak to pull it off? This article argues that Mearsheimer's evidence shows a selection bias, focusing on aggressive states in aggressive periods. To demonstrate my point, I examine four of the worst European crises between 1814 and 1848. Contrary to the claims of some scholars, 5 but consistent with both schools of realist theory, I show that the balance of power went on working in the Vienna era, and did much to restrain Russia, Prussia and especially France. At the same time, all three showed restraint, passing up gains that greedier or more reckless powers might have bid for. Had Mearsheimer examined this period, he could have reached quite different conclusions. The Concert of Europe's members were good defensive realists. But they responded to structural constraints as they did largely because their leaders and domestic regimes were cautious and moderate -in other words, for unit-level reasons.
Defensive realism, properly conceived, gives a better account of the Concert of Europe than its offensive counterpart. Neorealist theory predicts that states will seek to survive, 6 common sense predicts that they will seek to avoid military disaster, and Concert-era leaders sought to do both. Structural realism can explain Napoleon and Hitler only by assuming that they were not security-maximisers, but unusually greedy gamblers whom even great risks could not deter. 7 But defensive realism gains this explanatory power by smuggling liberalism in through the back door, exposing to attack from both offensive realist and liberal critics. 8 The solution, as Jeffrey Legro and Andrew Moravcsik have proposed, is explicitly to recognise that defensive 'realism' is a synthesis of realist and non-realist theories. Realism predicts that states will respond as security maximisers to structural incentives; other theories explain cases when they do not. 9

Eat or be eaten
For Mearsheimer, world politics is a jungle, and every great power a jungle cat. When there is a rough balance of power, they may hold each other in check. But now and then one state pulls ahead. In this situation of 'unbalanced multipolarity', it usually makes a run for regional hegemony. Most powers are too weak to try, but these 'still act offensively to amass as much power as [they] can, because states are almost always better off with more rather than less power'. The choice is to eat or be eaten. Even colossal gambles such as Hitler's can be reasonable, since blocking coalitions may not form in time, and 'the security benefits of hegemony are enormous' if they pay off. 10 Mearsheimer is not just saying that states seize opportunities to expand on the cheap. The debate between offensive and defensive realists is often cast as whether states seek to expand or try to preserve the status quo, 11 but this description of defensive realism is -or at any rate should be -a straw man. To claim that states would pass up cost-free opportunities for power and influence is alien to any form of realism, which emphasises self-help in an anarchic world. Nothing in the logic of defensive realism precludes limited opportunistic expansion, 12 particularly into power vacuums. Fareed Zakaria's finding that around the end of the nineteenth century '[t]he United States did not expand against strong states that posed a great threat . . . but largely against areas that were weak' 13 is just what defensive realism should predict. Whether a given act of aggression was reasonable or excessive may sometimes be a matter of opinion. But what unambiguously distinguishes defensive realists is their claim that because states generally balance would-be hegemons, bids to dominate a system of great powers are quixotic. 14 Unit-level factors, rather than the pressures of anarchy, explain wild gambles such as Hitler's.
In contrast to defensive realists, Mearsheimer remains consistently structural in his theory. He explicitly rejects the distinction between rational limited aggression and bids for hegemony, arguing that the latter can also be reasonable responses to systemic incentives. 15 Moreover, structure makes even states that cannot hope for hegemony ready to run big risks and pay high costs. Mearsheimer presents the cases of Japan from 1868-1945, Prussia/Germany from 1862-1945, the USSR from 1917-1991, Britain from 1792-1945 and the United States from 1800-1990, showing that all but Britain -separated from the Continent by the English Channelexpanded aggressively into its surrounding region. 16 US expansion was largely into a vacuum -consistent with defensive realism. If, on the other hand, Germany and Japan are the norm, defensive realists really do have problems.
Fortunately, Mearsheimer's case selection is biased. He focuses on history's bully boys at the expense of others such as post-Napoleonic France and Austria. What is more, he examines particularly aggressive periods in their histories. 17 This is partly because making potential and actual military power criteria for being a great power means excluding some states that exercise restraint. Most scholars consider Prussia a great power throughout the nineteenth century, but it enters Mearsheimer's book only when Bismarck takes the reins. Postwar West Germany -also left outlacked the military muscle to compete with the superpowers, but was this simply, as Mearsheimer claims, because American occupation prevented it from doing so? 18 An unbiased test would examine all states with the potential to become military powers, capturing both revisionist states that bought the weapons, and status-quo states that did not. 19 In the nineteenth century this would mean adding France, pre-unification Prussia, Austria and Russia. Mearsheimer might argue that Prussia and Austria, though considered great powers, were too weak to embark on aggression. But if so, this should also have been true of post-unification Italy, whose belligerence he cites in support of his theory. 20 Similarly, if Soviet behaviour counts as evidence, surely we should include the Russian empire -the strongest power in continental Europe for several decades after 1815.
In the following sections I examine four of the most dangerous crises between 1814 and 1848: the Polish-Saxon crisis at the Congress of Vienna, the Greek revolution of the 1820s, the outbreak of the Belgian revolution in 1830 and the Syrian crisis of 1840. In each case I focus on the states most likely to start a major war, and ask what stopped them from doing so. If Mearsheimer's theory is right, a potential hegemon should hold back only when faced by a deterrent threat at least as clear, potent and credible as Germany faced in 1914 and 1939. His predictions about other states' behaviour are harder to distinguish from those of defensive realism, since he claims that great powers do not 'charge headlong into losing wars or pursue Pyrrhic victories.' 21 Mearsheimer might try to explain restraint in any of these cases as a rational cost-benefit calculation. Nevertheless, even weaker states should be hungry predators constantly on the prowl. Certainly we should not find 'key leaders expressing satisfaction with the existing balance of power, especially when their state had the capability to alter it.' 22 In one sense, this article presents a hard test for Mearsheimer's theory, since this is a period widely thought to be characterised by status-quo states. But in another sense, these are easy cases, since by focusing on major crises I emphasise situations of conflict, while ignoring the possibility that in the Vienna system many potential disputes never arose at all. 23 Moreover, I focus on three land powers -Russia, Prussia and France -that Mearsheimer describes as highly aggressive in other periods. If even these three exercised self-restraint, this should also have been true of Britain and Austria, the poster-child of satisfied powers. And if the Congress era is a tough case for Mearsheimer, my case selection is scarcely more biased than his own. Poland, he diluted his support for Prussia, which had to settle for half of Saxony and fewer than half of its inhabitants. 24 Some authors hold that faced with a blocking coalition, the Prussians and Russians backed down. 25 As Paul Schroeder points out, however, Russia actually won its confrontation over Poland, while Prussia could not resist on its own. 26 The more interesting question is why the Russians did not seize the chance to start a war for hegemony in Europe. True, by Mearsheimer's criteria, Russia was not a potential hegemon, which must be both military and economic powerhouses. Yet while the Russian case does not test his theory directly, we can test his assumption that regional hegemony is so desirable that statesmen will run great risks if they believe they have a chance to gain it. As he himself observes, while 'explanatory power is the ultimate criterion for assessing theories . . . a theory based on unrealistic or false assumptions will not explain much about how the world works.' 27 Russia's only significant ally would have been Prussia, which was willing to fight but whose finances and military were weak. 28  The French seemed likely to be drawn into any showdown, and those in Vienna evidently thought the balance of power was in their favour. 31  While an official close to the king insisted to the Duke of Wellington that France could and would stand up to Russia so long as Britain did not oppose it, the Duke wrote that '[t]he desertion is immense, and the recruiting very slow indeed'. 33 The acting French foreign minister held that Paris could not count on public or military enthusiasm for a war in alliance with Austria, while the French minister in St Petersburg wrote that Russia's army would welcome a fight. 34 Nor is it clear how soon Britain would have entered a war. Foreign Secretary Castlereagh put on a brave face in public, and argued that he could stop a Russian invasion so long as the Low Countries were fortified. 35 But Liverpool made clear he did not consider Poland worth fighting over, and other cabinet members also opposed intervention. Castlereagh, like Liverpool, privately acknowledged that the British public would support war only if the Low Countries came under threat. In any case, 'Austria and Bavaria . . . would have to bear the first shock.' He seems to have been unsure whether Austria, Britain and France would prevail: according to Louis de Viel-Castel, he thought that if they could stave off war for two years, they could have more chance of winning. Castlereagh concluded the triple alliance on 3 January. London immediately decided to ratify it. 36 By this point, however, Alexander was already showing signs of compromise. Thus a window of opportunity opened in late 1814, when Prussia had already aligned with St Petersburg, but before peace with the United States freed British troops to fight in Europe, 37 and before London committed itself to aiding the Austrians and the French. The Russians did not jump through it.

Russia and the Polish-Saxon crisis
In sum, Britain would not enter a war until late in the game, and even then it was unclear which coalition would win. Russian and Prussian chances seem as good as those of the Triple Alliance a century later. 'No country . . . had such a great need of peace as England', writes Karl Griewank: none was so unprepared for war as France under the unconsolidated rule of the Bourbons . . . and Austria could also scarcely have wished for an armed altercation, in which at first it would have confronted Prussia and Russia essentially [ziemlich] alone. . . . Prussia and Russia . . . with their armies concentrated in central Europe, would probably have had an initial advantage, had they been prepared to attack.
The alliance succeeded, says Griewank, not because it faced Russia and Prussia down, but because Russia had no direct stake in the Saxon issue, and Prussia was neither prepared nor willing to fight on its own. 38 What really matters, however, is not the objective balance of power but how the Russians saw it. In their public statements, they were cocky indeed. 'The Russians speak already as if they ruled the world,' reported an Austrian informant. 'I know someone whom one of their ministers told that they had only one goal at present: to preserve the preponderance that they had acquired by so many sacrifices, efforts and successes in Europe'. 39 '. . . I have two hundred thousand men in the duchy of Warsaw', Alexander told Talleyrand. 'Let them drive me out if they can!' 40 He used much the same language with Metternich and Castlereagh. 41 Princess Bagration claimed that she had sought to talk Alexander round on the Polish-Saxon question. The tsar had replied 'that he was sticking with his decision; that he would go to Munich, then to Berlin, then to Warsaw, have himself proclaimed king of Poland, and that he was prepared if anyone wanted to resist him'. Other officials seemed similarly confident. 42 If Alexander assumed the title of Grand Duke of Warsaw, commented an unsigned memorandum approved by the tsar, he will have in any future contingency yet another means of keeping Austria at bay. His Majesty would have only to proclaim himself King of Poland to wage a war advantageously against Austria, or even to threaten her with this change, to keep her within her proper limits and to foil all her combinations against Russia. 43 When Alexander decided to compromise, he was said to have told his Russian companions that 'I could certainly decide the affair, as did Napoleon, by dispatching 500,000 men; but as I am not here for war, but to consolidate the tranquility of Europe, I am abandoning my demands, and shall settle for an indemnity of part of the Duchy'. 44 All this may have been bravado. But the Russians' internal correspondence also suggests that they saw themselves in a strong position. ' foreign ministers, Count Nesselrode, to his ambassador in Paris. 'She would find the support of England and France of no more than negative use. We have Prussia and five hundred thousand men; thus she will only be able to use friendly representations against us; if they fail, there will be nothing to do but to give in. . . .' 45 General Chernyshev was more cautious. 'Certainly Russia . . . with the huge resources that [Your Majesty's] foresight has created for her, possessing moreover the inestimable advantage, unique today in Europe, of having the genius of her sovereign at the head of her armies', he wrote to the tsar in November 1814: is the power that should least fear the resumption of hostilities. Thus it is not so much out of fear of war as from the lively desire to see our political course either gain us a glorious and stable peace . . . or in case of war to assure its success through allies who, far from fearing us, would have an interest in our success, that I have raised my voice to Your Majesty. 46 Though the following month Chernyshev expressed dismay at Russia's diplomatic isolation and certainty that France would enter any war against Russia, he remained confident that Petersburg would have Prussia on its side. 47 We thus have weak evidence from internal sources that Russian officials saw the balance of power as favourable, plus a wealth of public statements. While the latter could be bluster, they are so frequent and consistent that it seems likely they reflected real confidence. Prussian leaders doubted in the early fall of 1814, before they had firmly taken sides, that they and Austria could take on Russia together. Castlereagh seemed unsure of a war's outcome. In early December the Prussian official Staegemann wrote that he favoured a tough stance: Austria was weak, Britain was tied down in the New World, war would threaten the new French government, and a war in coalition with France would be unpopular in Germany. 48 Others judged the balance differently, but Russian leaders bent on expansion, especially when it promised European hegemony, might well have rolled the dice.

Russian restraint in the Near East, 1821-33
If great powers are as aggressive as Mearsheimer claims, Russia should have taken all it could get away with from its decaying neighbour, the Ottoman empire. Indeed, many have thought that that was what Russia was trying to do. In reality, between 1821 and 1833 Russia passed up three chances to seize Constantinople. In 1833 -and perhaps 1821 as well -fear of Western retaliation seems sufficient -though not necessary -to explain Russian restraint, but in 1829 the Russians chose peace even 45  though they expected no immediate resistance. A war of conquest would not have lacked danger, but a Hitler or Napoleon would surely have run the risk.
When a revolution broke out in Greece in 1821, Turkey retaliated by massacring Greeks and interfering with Russian shipping through the Straits. Petersburg sent an ultimatum to Turkey, and when the Porte refused to meet it, prepared for war. According to Harold Temperley, neither Austria nor Britain 'was in a position to make war or even to threaten any other Power desirous of making it.' Had Alexander gone to war in 1821, Schroeder notes, he had 'every prospect of an easy military victory. The worst that could have happened with regard to the other powers is that Britain would have declared her neutrality. The possibility of an anti-Russian coalition like that of 1854 was nil.' 49 Still, there is some evidence that Alexander feared that a war of conquest could bring Europe together against him. Though he may have flirted with the idea of a great power partition of the Ottoman empire, he decided to continue talks with Turkey. 50 Balance of power considerations thus may -or may not -be sufficient to explain Russian restraint, but Castlereagh and Metternich also succeeded in 'grouping' Alexander. Opposition to revolution and commitment to the Concert of Europe were at least as important as fear of Western balancing in holding the tsar back. Alexander told his foreign minister Ioannis Capodistrias the following year 'that the preference accorded to the Austrian system was due uniquely to the urgent and major necessity of maintaining repose in Europe and its only guarantee -unity among the cabinets'. An internal report prepared for Tsar Nicholas I in early 1826 noted that Alexander had decided to wait to use force due to 'the fear of altering the nature of his relations with the leading European powers, the danger of thus weakening the guarantees of the general peace', the fear of assisting revolutionaries, and the hope of gaining allied co-operation. 51 Russia's next chance to topple the Ottoman empire came in 1829, as its troops approached Constantinople at the end of the Russo-Turkish War. Though Britain's and France's ambassadors prepared to summon their fleets, their home capitals shied away from a showdown. London 'made worried declarations, but took no effective steps either to restrain Russia or to bolster up Turkey', while Paris sought to appease Russia with a proposal to partition the Ottoman empire. 52  The more decisive our successes, the milder, more conciliatory and more friendly Lord Aberdeen's language became.' Austria, they claimed, was no more capable of resistance. 53 Some think Russia did not take Constantinople for fear of Western retaliation, 54 but the most important officials did not anticipate immediate attack. 'The affair is in your hands', Nesselrode told the commanding general. Britain's and France's ministers in Constantinople could 'no longer do any good in the negotiations, and very little harm, when one considers the magnificent position in which we are placed by your victories'. Nicholas was similarly confident: In London, 'they see and no longer fear the collapse of the Ottoman empire and to see us the master of Constantinople. . . . But . . . let us be more calm, more modest, more generous and more consistent than ever; those are the triumphs I seek, and God preserve me from seeking any others. . . .' 55 Though the Russians believed, as Nesselrode told the tsar three and a half years later, that 'a single word from Your Majesty would have sufficed to erase Turkey from among the governments of Europe', Nicholas preferred 'the indefinite prolongation of the Ottoman empire' to the risk that it would be replaced by a new and stronger neighbour. 56 In a memorandum to a high-level committee on Near Eastern policy, Dmitrii Dashkov held that Russia needs not new acquisitions or the expansion of her borders, but their security and the spread of her influence among neighbouring peoples, and that . . . she can achieve more easily by prolonging the existence of the Ottoman empire. . . . There was a time when a partition of Turkey might enter into the secret calculations of Russian diplomacy. Today, when the borders of the Empire stretch from the White Sea to the Danube and the Araks, from Kamchatka to the Vistula, very few acquisitions can be of use to it. 57 One ground for Russia's satisfaction, to be sure, was the belief that its victory had already placed Turkey under its thumb, and it was better to dominate the empire than to destroy it. Petersburg also stopped short because it did not believe Russia could take all of Turkey if the empire collapsed. Instead, it would have to share the remains with the other powers, some of which might make relative gains. 58 Yet why could Russia not have taken the lion's share? Nicholas and Nesselrode did not anticipate immediate resistance. Rather, the foreign minister and other high officials feared that toppling the empire would lead to conflict over the long term. 'However resigned and powerless they may be at the present moment', Nesselrode wrote in an internal memorandum, 'we should soon see combinations arising against us whose consequences would inevitably kindle a general war in Europe'. 59 In foregoing short-term gains for fear of provoking long-run balancing, Petersburg was acting as defensive realists prescribe. Moreover, while Russia exacted some modest territorial gains on its Asian frontier with Turkey, fundamentally it 'was not interested in territorial expansion at this time, at least not in Europe', as Schroeder observes. 'All that we could wish for has been accomplished', Nicholas told his brother, 'and our guarantees are huge'. 60 Russia's intervention in Turkey four years later showed the same mix of deterrence and self-restraint. The viceroy of Egypt, Mehemet Ali, had invaded Syria and now threatened Constantinople. In desperation Turkey asked for aid against its rebellious vassal. Russian troops landed on the Bosphorus, and stayed for half a year. On 8 July 1833 the Russians concluded a defensive alliance with Turkey requiring the latter to close the Straits to warships. Two days later they left. In 1834 Russia agreed to speed up its evacuation of Turkey's provinces of Moldavia and Wallachia, which it had occupied since 1829, in exchange for a small slice of territory along the border with Georgia. 61 This time the Russians clearly worried about provoking a balancing coalition. Of the other great powers, only Britain and France protested against the intervention, and even they did not offer forceful opposition. All the same, the Russians believed that it would be dangerous to go too far. 'From the beginning', Nesselrode wrote: we have established the principle of appearing in the theatre of events solely as the Porte's auxiliaries and at the formal demand of the sultan. By this we have legitimated our action, and disarmed Europe. . . . But from the moment we changed our system and acted . . . not in favour of, but in spite of the Porte, we should be sure to unite all the powers against us, and from that time on our role would become difficult to maintain, unless we decided to devote all our resources to it [unclear word or words] plunge Russia into a general war. This is surely not the will of the Emperor.
Russia took pains to square Austria before and during the intervention, for, as the tsar's confidant General Paskevich wrote, '[i]f we go in on our own, we shall have all Europe as enemies'. 62 But again, the Russians were also easy to deter. 'What would I gain from the conquest of Turkey?' Nicholas asked one of his generals in late 1833. 'To station forces there? But would Austria allow me to do so? What advantages would there be from that for our Mother Russia, that is, for the provinces: Yaroslavl, Moscow, Vladimir and others? Poland is enough for me as it is.' When the Russian commander in Moldavia and Wallachia urged prolonging occupation of the provinces, Nesselrode questioned whether it would pay for itself and warned that in any case 'it is by no means the intention of the monarch to extend the borders of his empire to the Danube'. He wrote to the tsar that henceforth Russia's only aim in the Near East would be to preserve its existing treaties. Nicholas took a similar view. 'Not new conquests but the management of [Russia's] regions', he told his heir in 1835, 'should henceforth be your only concern'. 63 60  Hypocrisy? At this very time the Russians were conquering the Caucasus. But this is the kind of opportunistic expansion the logic of defensive realism predicts. Whereas they faced only weak adversaries in the Caucasus, further expansion into Europe would bring them into conflict with other great powers. There was no need to run such risks when they had already achieved defensible frontiers. 'Russia's geographical position is so favourable that it renders her practically independent, so far as her own interests are concerned, of events in Europe', Nicholas wrote in an internal memorandum at the beginning of the 1830s, 'she has nothing to fear; her frontiers are sufficient for her; she has nothing to desire in that respect. . . .' 64 With friendly neighbours, a prominent official wrote in 1838 to the crown prince, Russia was now 'free to follow the impulse of a magnanimous policy'. When Catherine II had come to power, Russia had faced threats from Poland and Turkey, the latter of which also blocked its access to the Black Sea. 'At that time, it sought to expand; today, it sees its sole glory in preserving and governing wisely the vast countries that it possesses, in fortifying more and more their indissoluble unity'. 65

Russia, Prussia and the Belgian crisis, 1830
Belgium's uprising against Dutch rule in 1830 caused what one historian calls 'the first major crisis of the post-Napoleonic period that actually threatened to develop into a major European war'. 66 While Austria and the Wellington cabinet in Britain deplored the Belgian revolt, neither was able to act itself. France, which might have aided Belgium -and did, later in the crisis -was divided, many of its forces were in Algeria and Greece, and those that remained were of doubtful reliability. 67 Of all the powers, Russia was most eager to intervene. Nicholas had personal ties and financial interests in the Netherlands, but his chief motives were ideological. He wanted to put down a revolt against a lawful sovereign that threatened the monarchies of Europe. Russia was short of funds and suffering a cholera epidemic. Yet it continued to mobilise troops until late November, and responsible officials predicted that by the end of the year they would be ready to act. 68 Many scholars have concluded that it was only a revolt in Poland that stopped the Russians from going to war. 69 Indeed, Nicholas wrote that he was prepared to act unilaterally if he had the chance. 70 But almost at the same time the Russians were telling the Dutch and the allies they would intervene only with the latter's consent. 71 The tsar, Nesselrode wrote the following year, had recognised that military intervention must be 'unanimous'. 72 Petersburg's military preparations seem to have aimed more at pressing forward the other powers, and preparing for multilateral intervention than in acting on its own. 73 Nesselrode held that Russia must cooperate with the Western powers in order to manage them. Nicholas, he wrote the next year, had agreed to take part in the London conference in order 'to keep England in the ranks of the alliance,' and, by involving the French, to draw their teeth as well. 74 But the Russian foreign minister also argued that allied consensus, particularly Britain's support, was needed to keep France in check, or to defeat it if war broke out. Prussia lacked enough troops even to put down the Belgians, and could hardly bear the brunt of a French onslaught alone. 75 Agreement, he later wrote, had 'seemed all the more necessary inasmuch as it was easy to foresee that an armed intervention by the Quadruple Alliance . . . would have to be prepared to encounter and combat . . . not only the Belgian revolutionaries, but the French ones as well.' 76 In a dispatch to his ambassador in Vienna, Nesselrode wrote that Paris's opposition had forced Nicholas to negotiate. 77 While Petersburg was forced to act multilaterally, this was due less to norms than to French deterrence.
Britain's refusal to countenance intervention may well have been enough to restrain the Russians. But even if Petersburg had gained London's consent, it could still not have acted without Berlin's. The road to Belgium lay through Prussia; it is hard to see how without Prussian cooperation the tsar could have mounted a land invasion, the only kind he considered possible that late in the year. 78 But Prussia had little desire to act against the Belgians. Here too the balance of power is sufficient to explain Berlin's restraint. France had indicated it would resist intervention, and Prussia knew it would bear the brunt of a clash. It needed soldiers to police the Rhineland, and it would be slower than France to mobilise its forces if the latter attacked. Prussia was also anxious to retain Britain's support, but feared that if it came to blows, Britain would support France. Berlin could not count on winning a war. 'You cannot demand that we should bring upon ourselves . . . a war with France,' its foreign minister, Christian Bernstorff, told the Dutch, 'as well as with four million Belgians, whom we should have to fight on our own'. No European power, wrote King Frederick William III, could take on France by itself. Well before Poland rose up, he turned down Holland's appeal for aid, citing the risk of French intervention. Bernstorff wrote that even if the strategic picture had been more favourable, war would sabotage the economy. 79 But domestic factors also held Prussia back. Reliance on a non-professional army made it ill-suited to offensive warfare. Berlin believed war would stir up radical passions, and that its troops were needed at home. In any case, after the Polish-Saxon crisis, Prussia was not attracted by foreign conquests. 'Regard for public opinion helped to make Prussia a defensive, rather than offensive, power', writes Lawrence Baack. '. . . Prussia did not want to conquer Germany by force. This was distasteful, as well as being inherently unrealistic.' Prussian officials believed the public to be against war unless France attacked them first. 80 'What do you expect?' Bernstorff's successor asked a Russian official in 1833. '. . . We cannot risk war with France unless the war becomes a national affair for us. We cannot undertake it, so long as the public offers no support.' 81 Prussia's leadership did not want to fight in any case. Expansion could stir up domestic unrest. Taught to hate war in his youth, as an adult Frederick William had only come to despise it more. In stark contrast to his famous predecessor Frederick II, the leitmotif of his foreign policy was the effort to preserve peace. 'We should start from the assumption,' the king wrote in October 1830, 'that the present political situation. . . . can only be considered collectively by the great powers; hence only they can specify the casus foederis.' Perhaps even France could be grouped, with Belgium proving an occasion 'to bind it again in solidarity with the other powers to uphold the status quo in Europe'. Bernstorff felt a sincere -though not unconditionalcommitment to the solidarity of the old anti-Napoleonic coalition, and agreed that Prussia should intervene only in agreement with its other members. 82 While an unfavourable balance of power is sufficient to explain Prussian restraint in 1830, it is probably not necessary. 83 Though Bismarck and his followers later charged that Prussia missed a chance to exploit the situation for its own ends, Baack observes: [t]his evaluation confuses the Prussia of 1830 with the Prussia of the 1860s and postulates a leadership that possessed an entirely different set of political values. The central fact is that Prussia at this time was a state of only moderate strength, and its leadership, although aware of the potential of the nation-state, thought primarily in European terms -that also happened to represent the interest of the state. Power was to be used responsibly and morally. No one wanted to unleash the naked drive for territorial aggrandizement that had nearly destroyed the European states decades earlier.
Capturing how power and preferences underpinned the post-Vienna order, Baack argues that Prussia's leadership was 'being realistic as well as idealistic and cosmopolitan.' 84 As France's ambassador wrote in early 1832, 'The Emperor of Russia will not succeed in inducing the Prussian Cabinet to adopt, [sic] either violent views or hostile measures. Here, all the advantages derived from the statu quo are fully appreciated and will not be forfeited.' 85

France and the Syrian crisis of 1840
In July 1840, Austria, Britain, Prussia and Russia ordered the viceroy of Egypt, Mehemet Ali, to withdraw from northern Syria on pain of military intervention. This decision outraged France, Mehemet Ali's patron, leading to what Schroeder calls 'the worst crisis in Europe since 1815'. Much of France demanded war. King Louis-Philippe and his prime minister, Adolphe Thiers, talked tough and began an arms build-up. By October Britain's prime minister, Lord Melbourne, was worried sufficiently to send France an ultimatum threatening war. Soon after, Louis-Philippe forced Thiers out and the worst of the crisis was over. 86 This decision was clearly dictated by the balance of power. As Louis-Philippe made clear, France was not prepared for 'a struggle of one against four'. The ministers of the army and the navy argued that France was unprepared, and even Thiers conceded in the end that France could not fight all of Europe. 'We did not want war,' recalled the interior minister, 'we did not aim at it, and among a thousand reasons, one was decisive: France was not ready, and could not be for eight to nine months.' 87 Nevertheless Thiers hoped a military build-up would extract concessions. If Mehemet Ali could hold out, 'having completed our armament, we shall negotiate at the head of our forces, and we shall perhaps make an advantageous peace'. 88 The prime minister -and apparently his cabinet colleagues -recognised that brinksmanship could lead to war instead. '[P]eople can get carried away', Thiers wrote in August, 'some British and French boats can quarrel [s'insulter] in harbour; the Viceroy can do something rash'. 89 The king, however, was unwilling to risk the confrontation spiralling out of control. 'I believe no one wants war, and I still think no one can start it', he told Thiers, '. . . But the dangerous thing is to have the same confidence that it cannot break out.' 90 Like Frederick William III, and '[u]nlike Thiers with his conception of Napoleonic glory', Louis-Philippe found war repugnant. 'War, even successful, is fatal! It is a dunghill exhaling corruption!' 91 Here, as throughout his reign, the king restrained a public champing at the bit.
After 1840 the French government sought to preserve the European status quo. Like Nesselrode and Bernstorff, France's new foreign minister and de facto head of government, François Guizot, repudiated the European aggressions and conquests of the eighteenth and early nineteenth centuries. In part this was for fear of offending Britain, or that other states would gain more than France from reshuffling frontiers. But Guizot also feared that war would bring domestic unrest and economic disruption, and in any case he was content with France's boundaries in Europe. Not every Frenchman was a Louis-Philippe or Guizot. Most remained eager to overturn the Vienna settlement, even if some believed it could be done only by peaceful means. But the buck stopped at the Tuileries palace. Louis-Philippe's hatred of war, fear of domestic instability and desire to have his regime recognised abroad made France's policy essentially conservative. 92

Conclusion
After 1815 the balance of power still played a major role. Above all, it restrained France, the only dissatisfied power. 93 While Alexander I was grouped in 1821, he also may have been deterred, and Russian officials were careful to avoid a blocking coalition in 1833. In Belgium, Schroeder is right that Petersburg had to act 'with and through its allies', 94 but this was not because it embraced multilateralism. Instead, Russia needed its allies, above all London, if it came to a showdown with France. Berlin in turn was unwilling to bear the brunt of a French attack. Britain and Russia may have been strong enough to impose their desires when they acted together, but Petersburg knew that aggression was likely to cause London to balance against it. Britain also held the balance in the Belgian crisis between France and Prussia; had either side committed aggression, London would surely have thrown its support to the other. As Branislav Slantchev observes, 'for every potentially contestable territory, there existed some coalition of states that had a clear interest in blocking undesirable changes'. 95 What Mearsheimer calls 'balanced multipolarity' did contribute to the peace and stability of the Vienna era.
Yet the great powers also responded readily to external constraints. 'All the powers were war-weary', observes Alan Sked: all of them intensely frightened by the thought of revolution. Most of them were preoccupied by domestic problems and most of them were territorially satiated states. This was true of Austria and Prussia. France, on the other hand, was for long periods diplomatically isolated and could do very little to disturb the European balance. Russia, who would have been much more capable of doing so, chose not to. 96 In Russia's case, this was partly because it had achieved defensible frontiers. In an 1828 memorandum approved by the tsar, Nesselrode argued that European conquests 'in extending [Russia's] territory would weaken her power.' 97 States can conclude that expansion will render their borders less defensible; when this is the case, rational security-seekers support the status quo or retrenchment.
But the great powers' restraint was also due to unit-level factors. Much of French society would have backed war in 1840, but the king feared it would lead to revolution. 98 Conversely, even if Prussia's leaders had wanted war in 1830, Prussian society would not have supported intervention. Public opinion played little role in Russia, but neither Alexander nor Nicholas shared Catherine II's ambition to put a Romanov on the throne in Constantinople. Both tsars, by nature and moral ethos, were averse to rampant aggression. Until 1833 Nicholas sought greater influence and modest territorial acquisitions from the Ottoman empire, but once he had achieved this, he rested on his laurels. 99 Tellingly, when the Vienna system collapsed, it was largely unit-level factors that brought it down. Whether one blames the Crimean War on Nicholas I's pigheadedness, British and French domestic politics or Turkish intriguing, clearly no big shift had occurred in the balance of power. While this war is often depicted as tragedy, a strong case can be made that it was a crime. 100 Kissinger gets it almost right in saying that 'The balance of power inhibits the capacity to overthrow the international order; agreement on shared values inhibits the desire to overthrow the international order.' 101 In reality, as time went by, Europe's great powers agreed less and less on values. But four of the five remained basically content with the status quo, and even France was not so bent on revenge as post-World War I Germany. 102 Once the Polish-Saxon crisis was past, territorial disputes seldom marred great-power relations. 103 The great powers had not lost all interest in expansion, but they were easy to deter. In 1815 Alexander I backed away from a war which might have brought him European hegemony, and which he probably thought he could win. While this does not falsify Mearsheimer's theory per se, it contradicts one of its underlying assumptions: that states are prepared to take big risks in the pursuit of regional dominance. In 1829 prominent Russian officials opposed taking Constantinople largely for fear of ill-defined long term conflict with the other powers. Contrary to Mearsheimer's predictions, they repeatedly expressed satisfaction, even in internal statements, with the European status quo. After 1815, Prussia was little inclined toward aggression. Louis-Philippe might have liked to revise the postwar settlement, but he was no Hitler, prepared to run huge risks to do so.
Offensive realists are right that states face incentives for expansion, and are often constrained by the international system. Defensive realists already recognise this, however, while acknowledging that unit-level factors sometimes make states act in ways not predicted by structure. Domestic factors just will not go away. Defensive realists err not in combining structural and unit-level theories, but in insisting on calling the whole amalgam 'realist'. Snyder's theory of over-expansion, for example, uses realism to determine how states should behave, and a theory of domestic politics to explain why they don't. 104 Realist theories should establish the external constraints and incentives states face, not monopolise explanations of international politics. As Waltz says, 'Just as market theory at times requires a theory of the firm, so international-political theory at times needs a theory of the state'. 105 Structure matters, but so does agency.
In the early nineteenth century Russia's huge population and repressive domestic policies made it seem threatening, much like China today. In reality, its leaders were mostly content to uphold the European status quo. Unfortunately, many Westerners mistook a bearish but essentially moderate power for a ravenous aggressor, feeding suspicions that would contribute to the Crimean War. It would be a true tragedy should assumptions rooted in structural determinism cause China to become the Russia of the twenty-first century.