Why did the Cold War start?
The Cold War started because the wartime alliance between the United States and the Soviet Union was held together only by the common threat of Nazi Germany. Once that threat was eliminated in 1945, fundamental ideological differences — capitalism versus communism, democracy versus single-party rule — combined with mutual suspicion, territorial disputes in Eastern Europe, and the atomic bomb's new reality made sustained cooperation impossible.
The Cold War's origins lie in the fundamental incompatibility of the American and Soviet systems — an incompatibility that had been temporarily masked by the necessity of defeating Hitler. Understanding why this rivalry became the defining conflict of the second half of the 20th century requires examining ideology, geopolitics, and the specific decisions made in the war's aftermath.
Ideological opposition was foundational. The Soviet Union was built on Marxist-Leninist ideology that viewed capitalism as an exploitative system destined to be overthrown by workers' revolution. The United States was built on liberal democratic principles that viewed communism as tyranny. Each system claimed universal validity and saw the other as an existential threat. This was not merely a geopolitical rivalry — it was a contest between two fundamentally different visions of human society.
World War II's end created the conditions for direct confrontation. The Soviet Red Army occupied Eastern Europe, and Stalin installed communist governments in Poland, Czechoslovakia, Hungary, Romania, and Bulgaria — both as a security buffer against future invasion (the Soviet Union had been invaded through Eastern Europe twice in thirty years) and as an expansion of the communist system. The West saw this as aggressive expansion; the Soviets saw it as defensive necessity.
The atomic bomb transformed the strategic landscape. America's nuclear monopoly (1945–1949) gave it enormous leverage but also terrified the Soviets, who raced to develop their own weapon. The bomb's existence made direct conflict between the superpowers potentially civilization-ending, channeling their rivalry into proxy conflicts and competition.
Specific events in 1946–1947 crystallized the conflict. George Kennan's 'Long Telegram' from Moscow articulated the case for containment. Winston Churchill's 'Iron Curtain' speech in Fulton, Missouri, warned of Soviet expansion. The Truman Doctrine (1947) committed the United States to supporting nations threatened by communism. The Marshall Plan (1948) poured American money into Western European reconstruction — both a humanitarian act and a strategic move to prevent communist influence. The Soviet blockade of West Berlin (1948–1949) and the formation of NATO (1949) formalized the division of Europe into rival blocs.
The Cold War started, in essence, because two immensely powerful nations with incompatible ideologies found themselves face to face across the ruins of World War II, each convinced that the other threatened its survival, and neither willing to yield.