Decolonization is the dissolution of empire. Between 1945 and 1975, the European colonial powers withdrew from most of Africa, Asia, and the Caribbean. Dozens of new states were formed. The map of the world was redrawn.
But dissolution is not always permanent. Some empires reformed under new names. The Russian Empire became the Soviet Union, which controlled most of the same territory until its own dissolution in 1991. The French Empire became the French Union, then the French Community, and finally a network of military bases, currency pegs, and trade agreements that preserved French influence under a different vocabulary.
Other empires dissolved incompletely. Britain retained fourteen Overseas Territories, fragments of empire that voted against independence. Portugal held onto Macau until 1999. The United States still administers Puerto Rico, Guam, and other territories acquired during its imperial period.
The dissolution of empire, in short, is rarely total. Something always remains: a military base, a currency union, a language, a legal system. Empires dissolve into influence. Influence is harder to dissolve than territory.