upon the largest German youth cohorts ever in explaining the rise of Nazism in Germany in the 1930s. The 1994 Rwandan genocide has also been analyzed as following a massive youth bulge. Youth bulge theory has been subjected to statistical analysis by the World Bank, Population Action International, and the Berlin Institute for Population and Development. Youth bulge theories have been criticized as leading to racial, gender and age discrimination. Cultural Geoffrey Parker argues that what distinguishes the "Western way of war" based in Western Europe chiefly allows historians to explain its extraordinary success in conquering most of the world after 1500: The Western way of war rests upon five principal foundations: technology, discipline, a highly aggressive military tradition, a remarkable capacity to innovate and to respond rapidly to the innovation of others and—from about 1500 onward—a unique system of war finance. The combination of all five provided a formula for military success....The outcome of wars has been determined less by technology, then by better war plans, the achievement of surprise, greater economic strength, and above all superior discipline. Parker argues that Western armies were stronger because they emphasized discipline, that is, "the ability of a formation to stand fast in the face of the enemy, where they're attacking or being attacked, without giving way to the natural impulse of fear and panic." Discipline came from drills and marching in formation, target practice, and creating small "artificial kinship groups: such as the company and the platoon, to enhance psychological cohesion and combat efficiency. Rationalist Rationalism is an international relations theory or framework. Rationalism (and Neorealism (international relations)) operate under the assumption that states or international actors are rational, seek the best possible outcomes for themselves, and desire to avoid the costs of war. Under one game theory approach, rationalist theories posit all actors can bargain, would be better off if war did not occur, and likewise seek to understand why war nonetheless reoccurs. Under another rationalist game theory without bargaining, the peace war game, optimal strategies can still be found that depend upon number of iterations played. In "Rationalist Explanations for War", James Fearon examined three rationalist explanations for why some countries engage in war: Issue indivisibilities Incentives to misrepresent or information asymmetry Commitment problems "Issue indivisibility" occurs when the two parties cannot avoid war by bargaining, because the thing over which they are fighting cannot be shared between them,