Answer:
The Russian Revolution
Step-by-step explanation:
The Russian Revolution happened during a very intense period in time, WW1.
Russia was losing a lot of land in former, but now annexed Poland.
The Russian Revolution turned the country into a socialist state and caused a Civil War while at it.
This changed a lot for the world, as it inspired silent socialist revolutionist in other countries to rise up against their colonizers such as French Indochina, Central America, Cuba, etc..
Russia, now known as the Soviet Union also had a Cold War with the greatest power the world has ever seen, The United States, which started from 1945 to 1991.
It wasn't a direct war between the two superpowers, but they funded smaller countries to fight against each other and fought against to see who had the better economic system.