in 1571 the mostly greek-populated island of cyprus was conquered by the ottoman empire, following the ottoman–venetian war (1570–1573). after 300 years of ottoman rule the island and its population was leased to britain by the cyprus convention, an agreement reached during the congress of berlin in 1878 between the united kingdom and the ottoman empire. britain formally annexed cyprus (together with egypt and sudan) on 5 november 1914 as a reaction to the ottoman empire's decision to join the first world war on the side of the central powers; subsequently the island became a british crown colony, known as british cyprus. article 20 of the treaty of lausanne in 1923 marked the end of the turkish claim to the island. article 21 of the treaty gave turkish nationals ordinarily resident in cyprus the choice of leaving the island within 2 years or to remain as british subjects.