1941: Tensions decrease - The Soviet Union and the United States ally against Nazi Germany in World War II. This forms the basis for the Grand Alliance.
1942: Tensions increase - The Allies defeat the German forces in the Battle of Stalingrad, and the tide of war begins to turn against Germany. However, the Soviet Union is suspicious of the Western Allies' motives and believes they are not providing enough support.
1944: Tensions decrease - The Allies agree to a plan for the invasion of Normandy, which signals their commitment to defeating Germany in Western Europe.
1945: Tensions decrease further - The Allies defeat Nazi Germany in May 1945, and the war in Europe comes to an end. The Soviet Union and the United States are the two major powers left standing.
1946: Tensions increase - The Soviet Union installs communist regimes in Eastern Europe and begins to expand its influence in Eastern Asia. The United States responds with the Marshall Plan, providing economic aid to Western European countries to rebuild their economies and prevent the spread of communism.
1948: Tensions increase sharply - The Soviet Union blockades West Berlin, and the United States responds with the Berlin Airlift, supplying the city from the air. The Cold War begins.
1950: Tensions increase - The Korean War begins, with the United States and its allies fighting against the Soviet Union and China. The war ends in a stalemate in 1953, but tensions between the superpowers remain high.
1961: Tensions decrease temporarily - The Kennedy-Khrushchev summit in Vienna results in a thaw in tensions, and the superpowers agree to a partial nuclear test ban.
1962: Tensions increase sharply again - The Cuban Missile Crisis brings the world to the brink of nuclear war. The crisis ends when the Soviet Union agrees to remove its missiles from Cuba in exchange for the United States agreeing not to invade Cuba.
1975: Tensions decrease - The Helsinki Accords are signed, which reaffirm the principles of European security and cooperation. The superpowers agree to respect each other's territorial integrity and to not use force against each other.
1989: Tensions decrease - The Berlin Wall falls, and communist governments in Eastern Europe collapse. The Soviet Union itself dissolves in 1991, ending the Cold War.