France's colonial ventures date back to the 16th century, when French explorers arrived in North America, the Caribbean and the northern tip of South America. Over the following four centuries, France conquered territories in North, West and Central Africa and, to a lesser extent, East Asia. Because of its key geographical position, northern Africa became particularly important for France. Taking advantage of the decline of the Ottoman Empire, the French captured Algiers in 1830 and used it as a platform for regional expansion. By the early 20th century, France had expanded its dominions in Central and West Africa to the modern states of Tunisia, Morocco, Mauritania, Senegal, Guinea, Mali, Ivory Coast, Benin, Niger, Chad, the Central African Republic and the Republic of the Congo. France's presence also extended to the coastal enclave of Djibouti, the island of Madagascar and other islands on the Indian Ocean.