dec 25, 1991 - Collapse of USSR

Description:

Most people consider the Collapse of the Soviet Union (USSR) to be the end of the cold war as it was the end of the largest communist state in the world.
This date marked the dissolution of the USSR into 15 republic states.

On December 25th, 1991 the Soviet hammer and sickle flag lowered for the last time over the Kremlin, thereafter replaced by the Russian tricolor. Earlier in the day, Mikhail Gorbachev resigned his post as president of the Soviet Union, leaving Boris Yeltsin as president of the newly independent Russian state.

https://history.state.gov/milestones/1989-1992/collapse-soviet-union