In 1990, after the fall of the Berlin Wall, U.S. president George H. W. Bush through his secretary of state James Baker promised Soviet premier Mikhail Gorbachev that in exchange for Soviet cooperation on German reunification, the Cold War era NATO alliance would not expand “one inch” eastwards towards Russia. Baker told Gorbachev: “Look, if you remove your [300,000] troops [from east Germany] and allow unification of Germany in NATO, NATO will not expand one inch to the east.”
In the following year, the USSR officially dissolved itself. Its own defensive military alliance (commonly known as the Warsaw Pact) had already shut down. The Cold War was over.