The period following WWII was a period of tension characterized by conflict at diplomatic, economic and all levels short of actual armed conflict between the principals on either side. The origins of the Cold War can be traced to conclusion of World War II and the disagreements between the USSR and the Western Powers. It was a direct result/consequence of the inability of the left and center to co-exist after the disappearance of the right. Beginning with the Yalta Convention in 1945, and continuing with the Potsdam Conference later that year, the United States and the United Soviet Socialist Republic became disillusioned with each other over the division of Europe. Mutual mistrust and conflicting interests prevented the Big Three from reaching a compatible agreement. The Soviet Union needed security, especially in Eastern Europe, to eliminate the threat posed by Germany. American feared another economic depression and required the European market. With the Soviet expansion in Eastern Europe the US might loose the market. Therefore, the United States sought free flow of capital and the "open door" economy. The communist ideology and the western reaction to it had not changed by the end of the World War II. Americans still believed that the Soviet Union was out for world domination, as she attempted to expand outside of Eastern Europe. This contributed to shaping the policy of "containment". The communistic ideology appeared desirable to outside inhabitants. As troops returned to their native countries following the end of the war, many were greeted with thoughts of displacement and unemployment. The ideas of guaranteed provisions and employment were alluring, despite the strings that accompanied them. Events before, and after the war, as well as conflicting ideologies and the U.S. military involvement in Japan as well as the prevailing military reality resulted in the inability of the Great Powers to solve those conflicts and led to the Cold War.