East Germany withdrew from the Pact following German reunification in 1990. On 25 February 1991, at a meeting in Hungary, the Pact was declared at an end by the defense and foreign ministers of the six remaining member states. The USSR itself was dissolved in December 1991, although most of the former Soviet republics formed the Collective Security Treaty Organization shortly thereafter. In the following 20 years, the Warsaw Pact countries outside the USSR each joined NATO (East Germany through its reunification with West Germany; and the Czech Republic and Slovakia as separate countries), as did the Baltic states which had been part of the Soviet Union.