and the Comoros. Madagascar became part of the French colonial empire following two military campaigns against the Kingdom of Madagascar, which it initiated after persuading Britain to relinquish its interests in the island in exchange for control of Zanzibar off the coast of Tanganyika, an important island hub of the spices trade. The British also held a number of island colonies in the region, including the extended archipelago of Seychelles and the rich farming island of Mauritius, previously under the French sovereignty. Atlantic Ocean islands There are two sovereign island nations in the Atlantic Ocean: São Tomé and Príncipe and Cape Verde. Both islands share some historical and demographic features, especially in relation to their uses as transit points during the Atlantic slave trade. Neither São Tomé and Príncipe nor Cape Verde were inhabited before European colonization in the wake of the Atlantic slave trade. European dependencies and territories Both Spain and France retain possession of a number of territories in Africa in the form of islands in the Mediterranean Sea of the Atlantic Ocean in the case of Spain, and in the Indian Ocean in the case of France. Italy, the United Kingdom and Portugal also retain possession of small islands in the Atlantic Ocean. The Canary Islands, as well as Ceuta and Melilla and the Plazas de soberania islands in the Mediterranean Sea off the northern coast of Morocco, have long been in Spanish possession since the Reconquista, although Morocco continues to challenge Spain's authority over some of the islands. Following the independence of Comoros from France, the island of Mayotte voted in 1975 to remain a French territory, and in 2011 attained the status of a French department, along with Réunion which has held that status since the 1950s. Comoros continues to challenge France's possession of Mayotte, and Comoros, Madagascar, Mauritius and Seychelles also variously dispute France's possession of its Îles Éparses, or other scattered islands of the Indian Ocean. The United Kingdom also retains territories in the form of Saint Helena, Ascension, and Tristan da Cunha off Africa's western seaboard in the Atlantic Ocean, as does Portugal with the islands of Madeira north of the Canary Islands and Italy with the islands of Lampedusa and Lampione off the northern coast of Tunisia. Other Many continental African countries also include many islands within their territories. Some of these islands have witnessed rising secessionist movements, most notably the