Correct answer: 4) World War II
Explanation:
After World War II, as the Cold War began, the Soviet Union influenced elections in Eastern Europe to make sure those nations fell under Communist control. The Soviets defended the establishment of such buffer states on the basis of how Germany had viciously invaded the USSR duriing World War II.
In response to expansion of Soviet influence and communism into Eastern Europe, the United States, along with Canada, joined with ten European countries in signing the North Atlantic Treaty in 1949. This created the North Atlantic Treaty Organization (NATO), which was a defensive military alliance of democratic states over against the expanding threat of communism felt in the Cold War environment. The ten original Western European members of NATO were the United Kingdom, France, Belgium, the Netherlands, Denmark, Norway, Portugal, Italy, Iceland, and Luxembourg.
Following the formation of NATO, the Communist bloc, led by the Soviet Union, responded. The Warsaw Pact was created as an alliance of Europe's Communist nations. The Warsaw Pact was given that name because the agreement was signed in Warsaw, Poland. Established in 1955, the Warsaw Pact included the Soviet Union, Albania, Bulgaria, Czechoslovakia, East Germany, Hungary, Poland, and Romania. The nations signing the treaty called on each other to defend of any member of the Pact that was threatened by enemy forces.