What event caused Russia to exit World War I?

1 Answer

The Russian Revolution

Explanation:

Russia, during WW1, suffered from huge losses, food shortages, high prices, and worker strikes. Things got so bad that the Tsar decided to abdicate his throne. He was placed, along with his family, under house arrest shortly thereafter.

This is a great resource for lots of detail:
https://en.wikipedia.org/wiki/Russian_Revolution