Not only did communist regimes bring revolutionary changes to the societies they governed, but their very existence launched a global conflict that restructured international life and touched the lives of almost everyone, particularly in the twentieth century’s second half. That rift began soon after the Russian Revolution when the new communist government became the source of fear and loathing to many in the Western capitalist world. The common threat of Nazi Germany temporarily made unlikely allies of the Soviet Union, Britain, and the United States, but a few years after World War II ended, that division erupted again in what became known as the cold war. Underlying that conflict were the geopolitical and ideological realities of the postwar world. The Soviet Union and the United States were now the major political/military powers, replacing the shattered and diminished states of Western Europe, but they represented sharply opposed views of history, society, politics, and international relations. Conflict, in retrospect, seemed almost inevitable.