Sultanate on the SE Arabian Peninsula, on the Gulf of Oman and the Arabian Sea. Its capital is Masqat. It was first Islamicized in the seventh century. In the 16th century it was subject to Portugal. The most powerful Arabian state in the early 19th century, it controlled Zanzibar and much of the coast of Persia. After its fall from power in the 19th century, it became dependent upon the British government. It has been the scene of constant civil strife in the 20th century, including a civil war in the Dhofar region during the 1960s. Oil was discovered in commercial quantities in 1964. In 1970 Sultan Said ibn Timer was deposed by his son, Qabus bin Said, who promised to use oil revenues for modernization. Oman joined the United Nations and the Arab League in 1971. In 1981, Oman and other Persian Gulf nations joined Saudi Arabia as founding members of the Gulf Cooperation Council. After the Iraqi invasion of Kuwait, Oman opened its bases to the international coalition forces against Iraq in the 1991 Gulf War. In 1996 the sultan issued a decree clarifying the royal succession, providing for a bicameral advisory council with some limited legislative powers and a prime minister, and guaranteeing basic civil liberties for Omani citizens. Military bases in Oman were used in 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.