The modern boundaries of Mozambique were not defined until the late 19th century. For centuries before, kings, chiefs, and warlords rose and fell, populations settled and moved on, and frontiers between competing societies constantly shifted. Mozambique's first inhabitants were Bushmen and Hottentot hunters and gatherers. Bantu-speaking peoples migrated to the area from the north, passing through the Zambezi River Valley into the plateau and coastal areas between the first and fourth centuries. By the time Arab traders first landed on Mozambique's offshore islands around A.D. 300, the indigenous peoples had been absorbed into Bantu society. Portuguese explorers reached Mozambique in 1498. From then on, Portuguese trading posts became regular ports of call for European ships on new trade routes to the East. Later, traders traveled inland seeking gold and slaves. It is estimated that nearly 1 million people were sold as slaves to French colonies, Brazil, Cuba, and North America. Mozambique was a Portuguese colony for nearly 500 years. The colonial policies of Lisbon were designed to benefit white settlers, members of elite Mozambican families, and Portugal. Little attention was paid to the development of Mozambique's economic infrastructure. What development did take place was linked to the powerful economy of neighboring South Africa through trade networks and the export of labor to South African mines. After World War II, while many European nations were granting independence to their colonies, Portugal clung to its overseas territories. In 1964, Front for the Liberation of Mozambique (FRELIMO), led by U.S.-educated Eduardo Mondlane, initiated an armed campaign against Portugal. After 10 years of sporadic warfare, Mozambique gained independence on June 25, 1975, with Samora Machel as president and the Marxist FRELIMO as the sole legal political party. A civil war between the FRELIMO government and the Mozambican National Resistance (RENAMO) began in 1976. RENAMO was initially supported by Ian Smith's apartheid regime in Rhodesia. After Rhodesia became the independent state of Zimbabwe in 1980, apartheid South Africa took over the sponsorship of RENAMO. Local populations in the central and northern regions, who were dissatisfied with the FRELIMO government, supported RENAMO despite its human rights abuses. In 1984 the governments of South Africa and Mozambique signed the Nkomati Accord, committing their countries to the cessation of hostilities. Despite the ensuing reduction in external support of RENAMO, the civil war continued. In 1986 President Machel was killed in a plane crash and was succeeded by Joaquim Chissano. An estimated 1 million people died during the war. In 1989 FRELIMO officially abandoned Marxist-Leninism under pressure from the International Monetary Fund and The World Bank to make a structural readjustment and open up to a market economy. In 1990 direct talks began between the government and RENAMO. Negotiations were proceeding slowly when, in 1992, Mozambique suffered its worst drought in the 20th century. The government and RENAMO subsequently agreed on principles for humanitarian assistance while pledging security for relief operations. A formal cease-fire went into effect on October 4, 1992, and a U.N. peacekeeping force oversaw a successful two-year transition to multiparty elections. By 1995 the more than 1.7 million refugees who had sought asylum in neighboring countries as a result of the war and drought returned to Mozambique as part of the largest repatriation witnessed in sub-Saharan Africa. At the same time, an additional 4 million internally displaced people returned to their areas of origin.