What happened
After failed reform, nationalist fragmentation, and political crisis, the Soviet Union ceased to exist as a state and its constituent republics moved into post-Soviet independence.
Why it matters
This is the formal terminus of the Cold War world. It ended the Soviet superpower state, cleared the way for a unipolar moment centered on the United States, and reshaped global politics, economics, and security debates.
Notes
Use this as the terminal event for the Cold War timeline.