The history of Tanzania begins with the dawn of our species. Most experts agree that the earliest humans originated in fertile regions of East Africa. Cushitic-speaking people from southern Ethiopia migrated through the eastern part of the Great Rift Valley into north central Tanzania during the first millennium B.C. Early cattle herders found an unoccupied niche in the virgin grasslands and coexisted with the Khoisan hunters and gatherers who were already there. During the first millennium A.D., Bantu-speaking peoples originating from west central Africa filtered into western Tanzania and the fertile volcanic mountains of the northeast. These iron-working cultivators preferred wetter areas and thus avoided the dry savannas that were already occupied by hunters, gatherers and pastoralists. Early residents of Tanzania's coastal region experienced heavy Eastern, rather than African, cultural influences, developing a different culture from the people living in the interior. Merchants from Egypt, Assyria, Phoenicia, Greece, India, Arabia, Persia, and China were already visiting this region during the first century A.D. By the ninth century, Arabs and Shirazi Persians were significant traders on the coast, and large numbers of them settled on the offshore islands. In time, the Arab and Shirazi communities intermingled with the Bantu-speaking mainland groups and a new culture - the Swahili - was born. During the late 19th century, European explorers and missionaries used Zanzibar as a point of departure for the mainland. Their travels helped define future colonial boundaries and paved the way for Protestant and Roman Catholic missionaries. In its desire to establish an economic and political foothold among other European powers, a newly unified Germany entered mainland Tanzania in 1884 and signed a series of agreements with local rulers that ceded administrative and commercial protection to Germany. With the onset of World War I, Germany lost control of mainland Tanzania. Great Britain took over and renamed the mainland Tanganyika. In 1922, the League of Nations consigned Tanganyika to the British Empire under its mandate system. It was not until 1961 that Tanganyika gained independence from Britain, with Julius Nyerere serving as the country's first president. In January 1964, revolutionary forces overthrew the sultan of Zanzibar, and three months later, the mainland and the islands of Zanzibar joined to become the United Republic of Tanzania.