While World War I tried to prevent future wars and outlaw using war as a form of foreign policy, the diplomats who developed the Treaty of Versailles at the end of war failed to do so. The treaty, finalized in 1919, featured several elements, such as the war guilt clause, which forced Germany to accept blame for the war. This resulted in Germany's humiliation and created the desire, over time, for Germany to regain its lost lands and recover its hurt pride. In addition, Germany had to pay massive reparations, or money, to the allies, causing it to fall into financial hardship that also made the Germans turn to Hitler and to fighting World War II. Finally, though the treaty created the League of Nations to police aggression between nations, the U.S. did not join the league, and it was largely powerless.
World War II resulted in many institutions to safeguard world peace, such as the United Nations. In addition, American policies such as the Marshall Plan gave money to rebuild Europe and Japan along peaceful, democratic means. However, the end of the war resulted in the growth of the Cold War between countries allied with the U.S. and countries allied with the Soviet Union. Many historians believe that, in part, the Soviet Union was motivated to instigate the Cold War because of the American show of power in dropping atomic bombs on Hiroshima and Nagasaki in 1945 at the war's end. The Soviet Union captured much of Eastern Europe as a buffer against future aggressions by Germany. Therefore, World War II also ushered in the Cold War rather than creating world peace.