views and rhetoric. Tensions with Yemen subsided only after 1967, when Egypt withdrew its troops from the country. Saudi forces did not participate in the Six-Day (Arab–Israeli) War of June 1967, but the government later provided annual subsidies to Egypt, Jordan, and Syria to support their economies. During the 1973 Arab-Israeli war, Saudi Arabia participated in the Arab oil boycott of the United States and other Western allies of Israel. A founding member of OPEC, Saudi Arabia voted in favor of the group's decision to moderate oil price increases beginning in 1971. After the 1973 war, the price of oil rose substantially, increasing Saudi Arabia's wealth and political influence. Faisal was assassinated in 1975 by his nephew, Prince Faisal bin Musaid, and was succeeded by his half-brother King Khalid, during whose reign economic and social development continued at an extremely rapid rate, revolutionizing the infrastructure and educational system of the country; in foreign policy, close ties with the US resumed. In 1979, two events occurred that the Al Saud perceived as threatening the regime, and had a long-term influence on Saudi foreign and domestic policy. The first was the Iranian Islamic revolution. There were several anti-government riots in the region in 1979 and 1980. The second event was the seizure of the Grand Mosque in Mecca by Islamist extremists. The militants involved were in part angered by what they considered to be the corruption and un-Islamic nature of the Saudi regime. Part of the response of the royal family was to enforce a much stricter observance of Islamic and traditional Saudi norms. Islamism continued to grow in strength. King Khalid died in June 1982 and was succeeded by his brother King Fahd in 1982. Fahd maintained Saudi Arabia's foreign policy of close cooperation with the United States and increased purchases of sophisticated military equipment from the US and Britain. Following the Iraqi invasion of Kuwait in 1990, Saudi Arabia joined the anti-Iraq coalition. King Fahd, fearing an attack from Iraq, invited soldiers from the US and 32 other countries to Saudi Arabia. Saudi and coalition forces also repelled Iraqi forces when they breached the Kuwaiti-Saudi border in 1991. In 1995, Fahd suffered a debilitating stroke and his half-brother, Crown Prince Abdullah, assumed day-to-day responsibility for the government. In 2003, Saudi Arabia refused to support the US and its allies in the invasion of Iraq. Terrorist activity within Saudi Arabia increased