system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The rivalry between Russia and the U.S.
gpt
This is complicated and I'll try to simplify it.
Before 1936 Russia had little to no relation with the US, during WWII different ideologies made them not allies but unite against the Nazis. At the ed of WWII there was a competition to see who could get the most scientist and research form the Nazis, so that became a direct confrontation. When WWII ended, there where only 2 strong countries, US and Soviet Union, since the rest were recovering from WWII, and both countries wanted as many other countries to follow their way of life since Soviet communism and US liberalism were not compatible. After that there were the wars of Korea, Vietnam and Afghanistan where each chose a side and gave them money, weapons and military advisers with the hope that their side would win making it a friendly country towards them. So basically they were the only two players and they both wanted to win.

I hope this helps a little a someone else can add to it.