The correct answer to this open question is the following.
Although there are no options attached, we can say the following.
Stalin failed to act quickly on promises to help the U.S., according to the agreements reached during the Yalta Conference and later in the Potsdam Conference. However, the United States also failed to do things agreed upon during the conferences. Of course, both nations have their own sides of the story. The real thing was that these series of disagreements contributed to mistrust between the nations.
During the so-called Cold War years, the Soviet Union remained in control of Czechoslovakia, East Germany, Romania, Bulgaria, Poland, and Hungary. Stalin considered these countries as a buffer in case the western allies tried to invade the Soviet Union.
The Cold War years was a time in which the United States and teh Soviet Union competed in the arms race, the space race, and in spreading/contain Communism in the world. These generated so many conflicts and wars around the world.
