The history of human habitation in Tanzania goes back almost two million years, and the fossils found at Olduvai Gorge by Louis and Mary Leakey now stand among the most important artifacts of the origins of our species. Artifacts of later Paleolithic cultures have also been found in Tanzania. There is evidence that communities along the Tanzanian coast were engaging in overseas trade by the beginning of the first millennium AD. By 900 AD those communities had attracted immigrants from India as well as from southwest Asia, and direct trade extended as far as China. When the Portuguese arrived at the end of the 15th century, they found a major trade center at Kilwa Kisiwani, which they promptly subjugated and then sacked. The Portuguese were expelled from the region in 1698, after Kilwa enlisted the help of Omani Arabs. The Omani dynasty of the Bu Said replaced the region's Yarubi leaders in 1741, and they proceeded to further develop trade. It was during this time that Zanzibar gained its legendary status as a center for the ivory and slave trade, becoming in 1841 the capital city of the sultan of Oman.
In Tanzania's interior, at about the same time, the cattle-grazing Maasai migrated south from Kenya into central Tanzania. Soon afterward the great age of European exploration of the African continent began, and with it came colonial domination. Tanzania fell under German control in 1886, but was handed over to Britain after WWI. Present day Tanzania is the result of a merger between the mainland (previously Tanganyika) and Zanzibar in 1964, after both had gained independence. Tanzania has like many African nations experienced considerable strife since independence, and its economy is extremely weak. However, political stability does appear to have been established in recent years.