One example could be the Russian October Revolution, which took place in November 1917 (the months are like this ebcause Russia used a different calendar). It was led by Vladimir Ilyich Ulyanov and it has brought socialism (bolsheviks communism) to the Eastern part of Europe, forming the USSR. The revolution overthrew the Romanov dynasty of Russian Emperors (Tsars).
The revolution was supposed to free the working class and put an end to the social injustice, but eventually it created on of the most brutal and tragic totalitarian system of the world.