The causes of World War 2
Ideology: both sides of the war felt their ideology was superior and given the previous situation in WW2, there was a tension that developed because of this and is one of the causes of the cold war.
The actions of the Soviet Union after WW2 had ended. It was understood that the countries helping to liberate the defeated would stay and help them install their government and leave. When the Soviets installed pro-Soviet communist governments the Allies felt it was similar behavior to that of Hitler and remained cautious.
Nuclear Weapons: After Hiroshima and Nagasaki, there was an expectation that militia should be able to compete with others. This created the arms-race.
The actions of the Soviet Union after WW2 had ended. It was understood that the countries helping to liberate the defeated would stay and help them install their government and leave. When the Soviets installed pro-Soviet communist governments the Allies felt it was similar behavior to that of Hitler and remained cautious.
Nuclear Weapons: After Hiroshima and Nagasaki, there was an expectation that militia should be able to compete with others. This created the arms-race.