International Conflict and Aggressive War
The concept of universal peace cannot exist without the notion of international conflict. As with any other diametrically opposed reference systems—unipolar/multipolar, status-quo/revisionist, identity/alterity, etc.—it is arguably less the phenomeno-hermeneutical study of these two conditions as individual occurrences than the nexus and antithetical relationship which exists between them which ultimately provides the most interesting avenues for scholarly research into their various subcategories. Since the ideal of universal peace is central to this dissertation's underlying historical analysis, a thorough engagement with its natural opposite therefore deserves particular attention. Two important qualifications, however, are in order: first, international war and conflict as here applied shall refer exclusively to wilful and aggressively pursued manifestations thereof, and thus not to the use of defensive war measures. While the latter designates the legitimate recourse to military force for the purpose of repelling an attack against the territorial integrity, political independence or interests of a political entity, its aggressive equivalent, on the other hand, represents the deliberate attempt of one unit to diminish or outright destroy the aforementioned, highly prized attributes of another. Secondly, it is important to remember that although a universal peace specifically implies the system-wide preponderance of both negative and positive peace elements, its possible termination, meanwhile, does not necessarily require the occurrence of universal war on a global scale—at least not initially. For even though the sudden outbreak of total systemic warfare would undoubtedly shatter world peace all by itself, its fragile composition might already become endangered by developments involving far less devastating and cataclysmic convulsions. History after all is rife with examples where the actual sources of transnational conflict are not just to be found in the eventual military clash of antagonists following a blatant breach of the peace by one of them.
Hence not only the political, cultural, socio-economic and institutional linkages of an increasingly interdependent global system, but also the unforeseeable ramifications of individual conflicts to international peace and security ought to feature as particularly relevant concerns in the maintenance of order and stability. In that regard, it matters not only whether conflicts arose over irrational fears, territorial claims, vested interests and/or overly assertive foreign policies. The very fact that disproportionate and excessively interest-driven ambitions pursued from an overly national(istic) standpoint are permitted to subsist at all may already be reason enough for why even in the absence of large-scale continental war the structural and normative foundations of world peace might always be in danger of gradual erosion. Put differently, the permanence and viability of universal peace not merely stands or fall with the resurgence of universal war; already the perceived necessity by some actors to revert to coercive action could not only constitute a threat to regional stability but likewise amount to an assault on the fundamental underpinnings of universal peace itself.
Conceptualizations of war and conflict are evidently a staple of numerous theories across the humanities and social sciences, thus only further underscoring the notion of their determinative influences on international history. Inter-state altercations are generally thought of having the most lasting and far-reaching impacts on the constellation of the international system. Yet very often the genesis of large-scale conflicts can just as well be traced back to comparatively smaller instances of organized violence such as civil wars, wars of secession, and struggles of national liberation. Also, the latter must not solely be interpreted in the light of one side trying to attain a relative advantage over the other. That is self-explanatory. More significant is the realization that such confrontations are also indicative of the still imperfect nature of the overarching systemic environment in which they occur. Specifically, they expose organizational flaws in the international architecture which have yet to be remedied and, for whatever reason, still allow for the emergence of regional strife that could easily degenerate into dangers of a much greater magnitude.
War as a phenomenon of human interactions of course cannot be divorced from political passions and calculations and therefore has "no meaning beyond the political" as Colin Gray remarks. Although the use of force can naturally be understood as learned behaviour and group norms to "reinforce, channel or deflect aggressive desires to dominate others," the political dimensions of such aggressive self-interest initiatives remain key to making sense of international conflict. Inter-state clashes of interests can issue from numerous concerns and considerations, albeit security fears and the advancement of material interests have regularly acted as the main factors in decisions that led to open conflict. Derived interests in regard to multilateral alliances and the geopolitical configuration of the international order are also often cited as major explanations for war. Finally, ideological justifications for promoting a particular world view or preserving actors' traditional way of life constitute another important aspect in the (re)-surfacing of transnational conflict.
Altogether, however, such observations do not reveal much about the specific causes of war. In that context, especially neo-realist scholars tend to locate the origins of wars not so much on the personal level of statesmen or on the domestic level of a country's political organization as above all on the structural level of the international system. By thus approaching global politics with different levels of analysis, their reflections have spawned a wealth of theories that primarily seek to explain aggressive state actions as "long-term conflicts of interest between the belligerents that are deeply imbedded in the larger structure of their relationship." Already E.H. Carr called attention to the systemic incompatibility between status-quo and revisionist powers, i.e. between those nations satisfied with the present distribution of national capabilities and those out to challenge it. This immanent tension as a result of an unjust international constellation is of major significance to any exploration of inter-state disputes, notably since, as Schweller points out, failure to acknowledge "the importance of revisionist goals (non-security expansion) as a driving force" likely accounts for the shortcomings of theories overly emphasizing safety concerns as the principal reason for conflictual tendencies. Indeed prominent defensive realists like Kenneth Waltz routinely suggested that the security dilemma, i.e. states' expectation that another nation's increase in security could translate into a decrease of its own security, is a perennial wellspring for state friction and anxiety.
On that note, however, Carr already stated that "wars begun for motives of security quickly become wars of aggression and self-seeking," an assessment which later aggressive realists, notably John J. Mearsheimer, further expanded upon by contending that great powers are "always searching for opportunities to gain power over their rivals, with hegemony as their final goal." While power is itself a fairly ambivalent concept, the notion of power distributions representing a major source of conflict cannot easily be dismissed. Especially when identifying power as the ability of one state to impose its will on another, plenty of tragedies infamously originated with one political entity trying to retain or augment its share of power. In particular attempts to shift the balance of power, or to prevent others from doing so, are apt to precipitate transnational disruptions and upheavals. Nonetheless it would be premature to conclude from this that a purported predisposition to power aggrandizement invariably has to form a core characteristic of international relations. After all, accepting conflict as an irrevocable corollary of inter-human association would not only render pointless any aspirations for peaceful change, but might also deflect from the actual and deeper causes for why some actors might choose to pursue destabilizing power maximization in the first place.
Above all the neo-liberal school of thought takes issue with such a pessimistic outlook on human progress and international cooperation. This can notably be seen in the shared understanding that, as Greg Cashew summarizes the neo-liberal position, "conflicts can be resolved through the use of law, the administration of good government, through democratic procedures and through negotiation, diplomacy and mutual agreement." Multilateral trade and cultural exchanges are argued to be especially well suited to ensuring inter-state harmony, notably as the commercial incentives for promoting the stability of the global market system seemingly outweigh any provocative national ambitions likely to risk the financial benefits thus accruing to states. Many realists, however, question the assumption that trade will invariably be held more efficient than military coercion for expanding states' markets or access to coveted commodities, especially as regards the equal application of that logic to both industrialized and non-industrialized countries. Also, it is by no means certain that states will value absolute over relative gains in their international dealings due to their fears that a competitor's economic power could be converted into additional military clout and political leverage. By the same token the mere installation of supranational institutions and organizations is likewise not believed to be a sure-fire guarantee against the occasional recrudescence of inter-state hostilities. Nor is the "democratic peace"-hypothesis, given that simply because democracies rarely go to war with each other, this "is not necessarily to say that democracies are more peaceful than other kinds of states."
 Gray, War, Peace and International Relations, pp. 8-9.
 On aggressive and defensive war see Michael Walzer, Just and Unjust Wars: A Moral Argument with Historical Illustrations (New York: Basic Books, 1977); Yoram Dinstein, War, Aggression and Self-Defence, 4th edition (Cambridge: Cambridge University Press, 2005); Cécile Fabre, Seth Lazar (eds.), The Morality of Defensive War (Oxford: Oxford University Press, 2014).
 Hitler Germany's successive violations of international peace settlements in the 1930s may be interpreted as a multi-phased cause of war eventually culminating the Second World War, as does Imperial Japan's progressive expansion in Far East Asia starting with Mukden incident in 1931. See Michael A. Barnhart , Japan Prepares for Total War: The Search for Economic Security, 1919-1941 (Ithaca, NY: Cornell University Press, 1987), pp. 77-214; Jürgen Förster, "Germany's Twisted Road to War, 1919-1939", in Frank McDonough, The Origins of the Second World War: An International Perspective (London: Continuum International, 2011), pp. 110-125. Likewise, the Balkan Wars and local imbalances are believed to having been an important precursor to the later conflagration of the First World War. See Richard C. Hall, The Balkan Wars 1912–1913: Prelude to the First World War (London: Routledge, 2000); Christopher Clark, The Sleep Walkers: How Europe Went to War in 1914 (New York, NY: Harper Collins, 2013), p. 242.
 See Douglas Woodwell, Nationalism in International Relations: Norms, Foreign Policy and Enmity (New York, NY: Palgrave Macmillan, 2007); Gretchen Schrock-Jacobsen, "The Violent Consequences of the Nation: Nationalism and the Initiation of Interstate War", The Journal of Conflict Resolution, Vol. 56:5 (October 2012), pp. 825-852; Michael Alan Brittingham, "The 'Role' of Nationalism in Chinese Foreign Policy: A Reactive Model of Nationalism and Conflict", Journal of Chinese Political Science, Vol. 12:2 (August 2007), pp. 147-166; Marlène Laruelle (ed.), Russian Nationalism, Foreign Policy and Identity Debates in Putin's Russia. New Ideological Patterns after the Orange Revolution (Stuttgart: ibidem-Verlag, 2014).
 Gray, War, Peace and International Relations, p. 1.
 Greg Cashman, What Causes War? An Introduction to Theories of International Conflict, 2nd edition (Lanham, MA: Rowman & Littlefield, 2004), p.1.
 Gray, War, Peace and International Relations, p. 19; Michael Howard, The Causes of Wars (Cambridge, MA: Harvard University Press, 1983), p. 22.
 Seyom Brown, The Causes and Prevention of War, 2nd edition (New York: St. Martin's Press, 1994), p. 19.
 Howard, The Causes of Wars, pp. 11-13.
 Jack S. Levy, "Theories of Interstate and Intrastate War. A Levels-Of-Analysis Approach", in Chester A. Crocker, Fen Osler Hampson, and Pamela Aall (eds.), Turbulent Peace: The Challenges of Managing International Conflict (Washington, D.C.: United States Institute of Peace Press, 2001), pp. 7-8.
 Brown, The Causes and Prevention of War, pp. 59-63.
 Ibid, pp. 53-58.
 See the next section for a more in-depth elaboration of the three levels of analysis.
 Brown, The Causes and Prevention of War, p. 65.
 Edward H. Carr, The Twenty Years' Crisis, 1919-1939 (London: Macmillan, 1939, 2001).
 Randall L. Schweller, "Neorealism's Status Quo Bias: What Security Dilemma?", Security Studies, Vol. 5:3 (Spring, 1996), p. 92.
 Kenneth N. Waltz, Theory of International Politics (New York, NY: McGraw Hill, 1979), pp. 105-107, 126; Kenneth N. Waltz, "The Origins of War in Neorealist Theory", in Robert I. Rotberg and Theodore K. Rabb (eds.), The Origin and Prevention of Major Wars (Cambridge: Cambridge University Press, 1988), p. 40. See also Charles L. Glaser, “The Security Dilemma Revisited", World Politics, Vol. 50:1 (October 1997), pp. 171–201.
 Carr, The Twenty Years' Crisis, p. 112.
 John J. Mearsheimer, The Tragedy of Great Power Politics (New York, NY: W.W. Norton, 2001, 2003), p. 29.
 For an excellent article on the role of different power types (hard power, soft power, structural power, etc.) in international relations, see Michael Barnett and Raymond Duvall, "Power in International Politics", International Organization, Vol. 59:1 (Winter 2005), pp. 39-75.
 Robert A. Dahl, "The Concept of Power", Behavioural Science, Vol. 2:3 (July 1957), pp. 202-203.
 Hans J. Morgenthau, Politics Among Nations: The Struggle for Power and Peace (New York: Alfred A. Knopf, 1978); Mearsheimer, The Tragedy of Great Power Politics, pp. 168-233; Brown, The Causes and Prevention of Wars, pp. 67-70.
 Kenneth N. Waltz, Theory of International Politics (New York, NY: McGraw Hill, 1979), pp. 102-129; R. Harrison Wagner, "Peace, War, and the Balance of Power", The American Political Science Review, Vol. 88:3 (Sep 1994), pp. 593-607; Michael Sheehan, The Balance of Power: History & Theory (London: Routledge, 2000); Paul Schroeder, "International Politics: Peace and War 1815-1914", in T.C.W. Blanning, The Nineteenth Century: Europe 1789-1914 (Oxford: Oxford University Press, 2000), pp. 158-208; David Sobek, The Causes of War (Cambridge: Polity Press, 2009), pp. 67-83.
 Some important neo-liberal works across a wide spectrum of subjects include Joseph S. Nye and Robert O. Keohane, Power and Interdependence: World Politics in Transition (New York, NY: Addison Wesley, 1977); Robert O. Keohane, International Institutions and State Power: Essays in International Relations Theory (London: Westview, 1989); Onora O'Neill, "Transnational Justice", in David Held (ed.), Political Theory Today (Stanford, CA: Stanford University Press, 1991), pp. 276-304; Michael W. Doyle, Liberal Peace. Selected Essays (London: Routledge, 2012).
 Cashman, What Causes War?, p. 170.
 See in particular Bruce Russett and John R. Oneal, Triangulating Peace: Democracy, Interdependence and International Organization (New York: W.W. Norton, 2001); Katherine Barbieri and Gerald Schneider, ”Globalization and Peace: Assessing New Directions in the Study of Trade and Conflict”, Journal of Peace Research, Vol. 36:4 (July 1999), pp.387-404.
 Levy, "Theories of Interstate and Intrastate War", pp. 11-12.
 Waltz, Theory of International Politics, pp. 105, 126; Joseph M. Grieco, "Anarchy and the Limits of Cooperation: A Realist Critique of the Newest Liberal Institutionalism", International Organization, Vol. 42: 3 (Summer 1988), pp. 498-500; Joseph M. Grieco , Cooperation among Nations: Europe, America, and Non-Tariff Barriers to Trade (Ithaca, NY: Cornell University, 1990), pp. 34-39.
 John J. Mearsheimer, "The False Promise of International Institutions", International Security, Vol. 19:3 (Winter 1994/1995), pp. 5-49.
 Levy, "Theories of Interstate and Intrastate War", p. 13; Sobek, The Causes of War, pp. 84-106.