Arab traders first began to colonize the area in 700 A.D. Portuguese explorers reached the coastal regions in 1500 A.D. and held some control until the 17th century, when the sultan of Oman took power. The Portuguese made Zanzibar one of their tributaries in 1503, but they were driven from Oman by Arabs in 1698. Zanzibar was declared independent of Oman in 1861 and, in 1890, it became a British protectorate.

With what are now Burundi and Rwanda, Tanganyika became the colony ofGerman East Africa in 1885. After World War I, it was administered by Britain under a League of Nations mandate and later as a UN trust territory.

In 1954, Julius Nyerere organized a political party, the Tanganyika African National Union (TANU). On December 9, 1961, Tanganika became an autonomous Commonwealth realm, and Nyerere became Prime Minister. On December 9, 1962, a republican constitution was implemented with Mwalimu Julius Kambarage Nyerere as Tanganyika's first president. Zanzibar became independent on December 10, 1963. On April 26, 1964, the nations merged into the United Republic of Tanganyika and Zanzibar. The name was changed to Tanzania six months later.

An invasion by Ugandan troops in November 1978 was followed by a counterattack in January 1979, in which 5,000 Tanzanian troops were joined by 3,000 Ugandan exiles opposed to President Idi Amin. Full-scale war developed. Julius Nyerere kept troops in Uganda in open support of former Ugandan president Milton Obote, despite protests from opposition groups.

On April 11, 1979, Idi Amin was forced to quit the capital, Kampala, ending the Uganda-Tanzania War. The Tanzanian army took the city with the help of Ugandan and Rwandan guerrillas. Amin fled into exile. By the middle of 1979, corruption reached epidemic proportions as the Socialist economy collapsed.

In October 1985, Nyerere handed power to Ali Hassan Mwinyi, but retained control of the ruling party, Chama cha Mapinduzi (CCM), as Chairman until 1990, when he handed that responsibility to Mwinyi.

One-party rule ended in 1995 with the first democratic elections held since the 1970s. Benjamin William Mkapa was sworn in as the new president on November 23, 1995.

On August 7, 1998, the U.S. embassy in Dar es Salaam was bombed by terrorists, killing ten. The same day an even more devastating explosion destroyed the U.S. embassy in neighboring Kenya.

President Benjamin William Mkapa sought to increase economic productivity while dealing with pollution problems and deforestation. In October 2000, Mkapa was easily re-elected.

In 2005 presidential elections, Jakaya Kikwete of the Chama Cha Mapinduzi Party won with 80% of the vote.

Prime Minister Edward Ngoyai Lowassa resigned in February 2008 over a scandal involving Richmond Development, an American energy company, which was hired to provide Tanzania with generators to supply electricity to the country during a power shortage. The company never began the operation, yet Lowassa urged the government to renew the contract. Mizengo Pinda replaced Lowassa as prime minister.

Jakaya Kikwete was re-elected president in November 2010.

In January 2011, police killed two during an anti-government protest in Arusha. The demonstrators demanded the release of opposition party leader Freeman Mbowe, who was detained ahead of a rally against government corruption

In May 2012, President Kikwete fired six ministers after the inspector of public finances noted the misuse of funds in at least seven ministries.

In October 2012, police arrested 126 people over attacks on five churches in Dar es Salaam. Muslims vandalised and torched the churches after a Christian boy was accused of urinating on a copy of the Koran.