Question

how did the United States and Soviet union go from allies during the second row for to enemies engaged in the cold war?

Answer 1

After the bombing of Hiroshima, the SU (I will refer to Soviet Union as SU and the USA as USA) feared that the USA would use the bombs against them. Also, tensions grew when Germany was split into West and East Germany. Berlin was also split and people went from East to West, becaus the West was extremely prosperous. In fact, it was so prosperous compared to the East, that a lot of people moved to the west and stayed. So, SU ordered a wall to be built so that East couldn't move to the West. Also, at the time, East berlin was still recked from WW2 and was out of money, since the SU spent all of its $$$ on the Space Race, which they kinda lost. Watch Oversimplified's Cold War video for more information. It's a great video.