There is disagreement among historians regarding the starting point of the Cold War. While most historians trace its origins to the period immediately following World War II, others argue that it began towards the end of World War I, although tensions between the Russian Empire, other European countries and the United States date back to the middle of the 19th century.

As a result of the 1917 Bolshevik Revolution in Russia (followed by its withdrawal from World War I), Soviet Russia found itself isolated in international diplomacy. Leader Vladimir Lenin stated that the Soviet Union was surrounded by a "hostile capitalist encirclement", and he viewed diplomacy as a weapon to keep Soviet enemies divided, beginning with the establishment of the Soviet Comintern, which called for revolutionary upheavals abroad.

Subsequent leader Joseph Stalin, who viewed the Soviet Union as a "socialist island", stated that the Soviet Union must see that "the present capitalist encirclement is replaced by a socialist encirclement." As early as 1925, Stalin stated that he viewed international politics as a bipolar world in which the Soviet Union would attract countries gravitating to socialism and capitalist countries would attract states gravitating toward capitalism, while the world was in a period of "temporary stabilization of capitalism" preceding its eventual collapse.

Several events fueled suspicion and distrust between the western powers and the Soviet Union: the Bolsheviks' challenge to capitalism; the 1926 Soviet funding of a British general workers strike causing Britain to break relations with the Soviet Union; Stalin's 1927 declaration that peaceful coexistence with "the capitalist countries . . . is receding into the past"; conspiratorial allegations in the Shakhty show trial of a planned French and British-led coup d'etat; the Great Purge involving a series of campaigns of political repression and persecution in which over half a million Soviets were executed; the Moscow show trials including allegations of British, French, Japanese and German espionage; the controversial death of 6-8 million people in the Ukrainian Soviet Socialist Republic in the 1932-3 Ukrainian famine; western support of the White Army in the Russian Civil War; the US refusal to recognize the Soviet Union until 1933; and the Soviet entry into the Treaty of Rapallo. This outcome rendered Soviet–American relations a matter of major long-term concern for leaders in both countries.