The Soviet Union, in East Germany, blockaded all rail, road, and water communications between Berlin and the West on July 24th of June in protest of the Allies banding together and making a new form of currency and uniting their occupation zones into one economic unit. On July 26th, the Allies brought food and other vital supplies to Berlin by air, creating a large amount of tension between the Allies and the Soviets. This is significant because this was one of the first major rivalry moments between the Soviets and the Allies- the two avoided war, but the Soviets cut off all communication for them.
During the Korean War, the Soviets and the Allies, yet again, opposed each other, causing lots of tension. The United States side with South Korea and helped against the North Koreans' advance, while the Soviet Union provided materials and medical services, along with planes and pilots, to the North Koreans. This war was significant because the Soviets and the United States supported opposing sides in the war, causing lots of tension. The United States' side won the war, causing lots of unrest and tension to rise for the Soviet Union.
The Space Race was the start of a true rivalry between the United States and the Soviet Union. The two countries raced each other to gain the advantage in space. At first, the Soviets had it- they sent the first human into orbit, the first satellite into orbit, and the first dog into orbit. However, the United States came back in the race by being the first to get a human on the moon. This race continued for many years throughout the Cold War, and even somewhat continues today. This race to prove their superiority throughout the Cold War was yet another way for tension to rise, and both sides started developing spacecraft that could help in war.
The United States flew a U-2 Reconnaissance plane over the Soviet Union, and it was shot down. It led to a conference with the Soviets that was very embarrassing for the United States, since they lost an American pilot in Soviet territory and had to go talk to the very suspicious Soviets. This caused lots of distrust between the two powers.
The United States sent 1500 CIA-trained Cuban exiles to the Bay of Pigs in Cuba, to try to overthrow Fidel Castro, and failed miserably at it. The countries' battle, which got lost horibly, caused the countries to get closer to a full-on war.
Reagan visited the Berlin Wall on August 12th, 1961. This event was extremely important because it showed both the Soviets and Germany that he and the United States were committed to keeping Communism out and keeping Berlin and the rest of Germany free.
The Cuban Missile Crisis happened when the United States and the Soviet Union got into a very tense standoff (political and military) over the installation of Soviet missiles in Cuba. This was extremely significant because this standoff was the closest that the United States and the Soviet Union ever got to war.
The two Strategic Arms Limitation Talks were the United States' and the Soviet Union's attempt to reduce the influence and amount of weapons that were made and used in the Cold War. The two talks led to treaties being made to limit the amount of nuclear warheads, for example. This is significant because the treaties led to the limitation of arms for both sides, drastically lessening the amount of destruction that could have taken place in the war.
The Soviets invaded Afghanistan to help the government there against the anti-communist guerrillas in the area trying to overthrow the government. The United States helped the guerrillas, and yet again another war had the United States and the Soviets fighting against each other. Again, the tension rose between the two nations.
Germany finally got reunified after the war in 1990. The two sides finally came together, causing the split country to finally reunify. This reunification was very significant because it brought about the end of the war in Berlin, and also showed that capitalism started to win the war over communism. The United States started to pull ahead of the Soviet Union, pulling capitalism forward with them.