Arms race to space race
At the end of world war II, nuclear weapons had been used for war. By 1949, the USSR had successfully tested their own atom bomb. Everyone scrambled to build rockets that could launch their terror weapons at any part of the globe, especially at each other. The same rockets being built for war were used to reach into space.
Here are a few videos on specific impulse, with much clearer explanations than ours.
Here’s a site about the space race.