West Germany, officially the Federal Republic of Germany or FRG (German: Bundesrepublik Deutschland or BRD), was proclaimed May 23, 1949 and included the post-World War II UK, US, and French occupation zones. West Germany joined NATO on May 9, 1955, and thus became a focus of the Cold War with its juxtaposition to Warsaw Pact member East Germany (the former capital, Berlin, was also divided but was completely within East Germany).
After the fall of the Berlin Wall on November 9, 1989, the unification of the two Germanys was quickly arranged: formally, West Germany grew by absorbing the territory of East Germany, and is now known simply as Germany. This took place on October 3, 1990, and the four occupying powers officially withdrew on March 15, 1991.
