How did Allied conferences determine the outcomes of the two world wars?
The outcome of World War I as set forth in the Treaty of Versailles helped set the stage for the war that would follow.
The causes of World War I are many and complex, and help explain how the confrontation took on the staggering proportions that it did. European great power politics, to which all the major actors were guilty to one degree or another, became so intricately linked that, when the Archduke Ferdinand was assassinated, it was merely the spark that set the continent ablaze.
By the time the war was over, the defeated, Germany, was subjected to an austere set of conditions designed to keep it in an inferior position relative to Britain and France. Those conditions, set out in the Treaty of Versailles, required Germany, an already defeated nation, to make large reparations payments to the victors, to cede control over large portions of territory that held large populations of Germans, and was restricted in its ability to rebuild its armed forces.
Russia, a "victorious" party to the war, was in the midst of revolution and civil war and was, consequently, in no condition to remain engaged on the Germany issue.
As World War II was drawing to a close a quarter of a century after the signing of the Treaty of Versaille, the situations of all the major actors had changed dramatically. Great Britain, while victorious, was financially broken and preparing for the loss of its empire; France had been occupied throughout the war and was similarly a defeated, if victorious in war, nation. Germany, of course, was in rubbles following years of sustained aerial bombing from the British and the United States on one side and from the brutal push into Berlin by the Red Army. In the end, only the United States and the newly emergent Soviet Union possessed the military and, consequently, political power to determine the post-war arrangements.
Those arrangements, initially negotiated in February 1944 at the Crimean city of Yalta by President Roosevelt, Prime Minister Churchill, and General Secretary Joseph Stalin, involved the division of Germany and Austria into spheres to be controlled by each of the four countries -- U.S., U.S.S.R., France, and Great Britain. As the western half of Germany would ultimately devolve to U.S. responsibility, and with the eastern half of the country under Soviet occupation, the front-lines of the Cold War were firmly established.