Ancient settlements in Oman, initially associated with nomads, date back to c.6000 B.C. Beginning in the 6th cent. B.C. and for roughly a millenium thereafter, much of coastal Oman was dominated by Persia (under the Achaemenids and Sassanids) and Parthia. Sumhuram, ruins in S Oman near modern Salalah, was founded (late 1st cent. B.C.) as a port in the frankincense trade and was closely linked to ancient Sheba. In the 6th cent. A.D. the region converted to Islam, and was successively controlled by the Umayyads, Abbasids, Karmathians, Buyids, and Seljuk Turks. Much of the coast of Oman was controlled by Portugal from 1508 to 1659, when the Ottoman Empire took possession. The Ottoman Turks were driven out in 1741 by Ahmad ibn Said of Yemen, who founded the present royal line.
In the late 18th cent., Oman began its close ties with Great Britain, which still continue. In the early 19th cent., Oman was the most powerful state in Arabia, controlling Zanzibar and much of the coast of Iran and Baluchistan. Zanzibar was lost in 1856, and the last Omani hold on the Baluchistan coast, Gwadar, was ceded to Pakistan in 1958. The sultan of Oman has had frequent clashes with the imam (leader) of the interior ethnic groups. In 1957 the groups revolted but were suppressed with British aid. Several Arab countries supporting the imam charged in the 1960s that the sultan's regime was oppressive and that the British were exercising colonial influence in Oman.
In 1965 the United Nations called for the elimination of British influence in Oman. In 1970, Sultan Said ibn Timer was deposed by his son, Qabus bin Said, who promised to use oil revenues for modernization. Rebel activity continued until the mid-1970s, however, particularly in Dhofar, in the south, where a Chinese-aided liberation front was strong. Oman joined the United Nations and the Arab League in 1971, but it did not become part of the Organization of Petroleum Exporting Countries (OPEC). In 1981, Oman joined Persian Gulf nations and Saudi Arabia in founding the Gulf Cooperation Council (GCC) and has since sought to promote ties among the participating nations.
Relations between Oman and the United States have been close since the 1970s. However, Oman did not establish full diplomatic relations with its neighbor Southern Yemen until 1983 and with the Soviet Union until 1985. As a result of the Iraqi invasion of Kuwait in Aug., 1990, Oman opened its bases to international coalition forces against Iraq in the 1991 Persian Gulf War. In 1996 the sultan issued a decree promulgating a new basic law that established a procedure for choosing the royal successor, provided for a bicameral advisory council with some limited legislative powers and a prime minister, and guaranteed basic civil liberties for Omani citizens. Military bases in Oman were used (2001) by U.S. forces involved in ground raids against Afghanistan and Osama bin Laden. In 2003 the lower house of the advisory council was freely elected for the first time. In the first half of 2011, Oman, like many other Arab nations, experienced antigovernment protests; in response, the sultan offered some economic concessions and political reforms, but dissent and discontent, in the form of strikes and protests, continued to fester on a small scale.