Why was World War II followed so quickly by the Cold War?

In 1945 the Allies faced the momentous challenges of rebuilding a shattered Europe, dealing with Nazi criminals, and creating a lasting peace. Reconstruction began and war crimes were punished, but the Allies found it difficult to cooperate in peacemaking. Motivated by different goals and hounded by misunderstandings, Great Britain and the United States on one side found themselves at loggerheads with the Soviet Union (U.S.S.R.). Though a handful of countries maintained a neutral stance, by 1949 most of Europe was divided into East and West Blocs allied with the U.S.S.R. and the United States, respectively. For the next forty years, the competing superpowers engaged in the Cold War, a determined competition for political and military superiority around the world.