strategies of cooperation and aggression. As peace makers became richer over time, it became clear that making war had greater costs than initially anticipated. One of the well studied strategies that acquired wealth more rapidly was based on Genghis Khan, i.e. a constant aggressor making war continually to gain resources. This led, in contrast, to the development of what's known as the "provokable nice guy strategy", a peace-maker until attacked, improved upon merely to win by occasional forgiveness even when attacked. By adding the results of all pairwise games for each player, one sees that multiple players gain wealth cooperating with each other while bleeding a constantly aggressive player. Socialism and managed capitalism Socialist, communist, and left-wing liberal writers of the 19th and 20th centuries (e.g., Lenin, J.A. Hobson, John Strachey) argued that capitalism caused war (e.g. through promoting imperial or other economic rivalries that lead to international conflict). This led some to argue that international socialism was the key to peace. However, in response to such writers in the 1930s who argued that capitalism caused war, the economist John Maynard Keynes (1883–1946) argued that managed capitalism could promote peace. This involved international coordination of fiscal/monetary policies, an international monetary system that did not pit the interests of countries against each other, and a high degree of freedom of trade. These ideas underlay Keynes's work during World War II that led to the creation of the International Monetary Fund and the World Bank at Bretton Woods in 1944, and later of the General Agreement on Tariffs and Trade (subsequently the World Trade Organization). International organization and law One of the most influential theories of peace, especially since Woodrow Wilson led the creation of the League of Nations at the Paris Peace Conference of 1919, is that peace will be advanced if the intentional anarchy of states is replaced through the growth of international law promoted and enforced through international organizations such as the League of Nations, the United Nations, and other functional international organizations. One of the most important early exponents of this view was Alfred Eckhart Zimmern, for example in his 1936 book The League of Nations and the Rule of Law. Trans-national solidarity Many "idealist" thinkers about international relations – e.g. in the traditions of Kant and Karl Marx – have argued that the key to peace is the growth of some form of solidarity between peoples (or