Between 1945 and 1955, the United States and the Soviet Union moved from wartime allies to Cold War adversaries. Initially, after World War II, the United States and the USSR worked together to ensure post-war stability and establish the United Nations. However, tensions between the two countries began to rise due to ideological differences and mutual suspicions.
During this period, the United States and the USSR engaged in an arms race, each trying to develop more advanced nuclear weapons. This resulted in a military buildup on both sides, which increased the risk of conflict. Additionally, the United States implemented the Truman Doctrine and the Marshall Plan, aimed at containing the spread of communism, which the USSR saw as a direct threat to its security and interests.
In 1948, the Soviet Union blockaded Berlin, leading to a standoff with the United States and its allies. The Korean War in 1950 further heightened tensions between the two countries. However, in 1955, the USSR and several Eastern European countries formed the Warsaw Pact, a military alliance aimed at countering NATO, which the United States and its allies had formed in 1949.
Overall, during this period, the United States and the USSR moved further away from each other, as their ideological differences and military buildups increased the risk of international conflict. The establishment of rival military alliances further contributed to this trend.