The Delegates from 27 nations (delegates representing 5 nationalities were for the most part ignored) were assigned to 52 commissions, which held 1,646 sessions to prepare reports, with the help of many experts, on topics ranging from prisoners of war to undersea cables, to international aviation, to responsibility for the war. Key recommendations were folded into the Treaty of Versailles with Germany, which had 15 chapters and 440 clauses, as well as treaties for the other defeated nations. The five major powers (France, Britain, Italy, the U.S., and Japan) controlled the Conference. Amongst the "Big Five", in practice Japan only sent a former prime minister and played a small role; and the "Big Four" leaders dominated the conference. The four met together informally 145 times and made all the major decisions, which in turn were ratified by other attendees. The open meetings of all the delegations approved the decisions made by the Big Four. The conference came to an end on 21 January 1920 with the inaugural General Assembly of the League of Nations. Five major peace treaties were prepared at the Paris Peace Conference (with, in parentheses, the affected countries):  The major decisions were the establishment of the League of Nations; the five peace treaties with defeated enemies; the awarding of German and Ottoman overseas possessions as "mandates", chiefly to members of the British Empire and to France; reparations imposed on Germany, and the drawing of new national boundaries (sometimes with plebiscites) to better reflect the forces of nationalism. The main result was the Treaty of Versailles, with Germany, which in section 231 laid the guilt for the war on "the aggression of Germany and her allies". This provision proved humiliating for Germany and set the stage for very high reparations Germany was supposed to pay (it paid only a small portion before reparations ended in 1931). As the conference's decisions were enacted unilaterally and largely on the whims of the Big Four, Paris was effectively the center of a world government during the conference, which deliberated over and implemented the sweeping changes to the political geography of Europe. Most famously, the Treaty of Versailles itself weakened the German military and placed full blame for the war and costly reparations on Germany's shoulders, and the later humiliation and resentment in Germany is often sometimes considered by historians to be one of the direct causes of Nazi Party's electoral successes and one of the indirect causes of World War II. The League of Nations proved controversial in the United States since critics said it subverted the powers of the US Congress to declare war; the US Senate did not ratify any of the peace treaties and so the United States never joined the League.