After World War II ended in 1945, Europe was divided into Western Europe and Eastern Europe by the Iron Curtain. Western Europe promoted capitalist democracies, and Eastern Europe came under the Communist influence of the Soviet Union
Answer: Yalta Conference (February 1945): Franklin Delano Rooselvelt, Winston Churchill, Joseph V. Stalin.
Explanation: terms "eastern" and "western" are of course geographical terms, but the question implies a politico-ideological division. Such a division took place in Yalta (1945) and later was corroborated later on with the Marshall Plan.