Saudi Arabia is the birthplace of Islam and home to Islam's two holiest shrines in Mecca and Medina. The king's official title is the Custodian of the Two Holy Mosques. The modern Saudi state was founded in 1932 by ABD AL-AZIZ bin Abd al-Rahman Al SAUD (Ibn Saud) after a 30-year campaign to unify most of the Arabian Peninsula. One of his male descendants rules the country today, as required by the country's 1992 Basic Law. King SALMAN bin Abd al-Aziz ascended to the throne in 2015 and placed the first next-generation prince, MUHAMMAD BIN NAYIF bin Abd al-Aziz, in the line of succession as Crown Prince. Following Iraq's invasion of Kuwait in 1990, Saudi Arabia accepted the Kuwaiti royal family and 400,000 refugees while allowing Western and Arab troops to deploy on its soil for the liberation of Kuwait the following year. The continuing presence of foreign troops on Saudi soil after the liberation of Kuwait became a source of tension between the royal family and the public until all operational US troops left the country in 2003. Major terrorist attacks in May and November 2003 spurred a strong on-going campaign against domestic terrorism and extremism. King ABDALLAH from 2005 to 2015 incrementally modernized the Kingdom - driven by personal ideology and political pragmatism - through a series of social and economic initiatives, including expanding employment and social opportunities for women, attracting foreign investment, increasing the role of the private sector in the economy, and discouraging businesses from hiring foreign workers. The Arab Spring inspired protests - increasing in number since 2011 but usually small in size - over primarily domestic issues among Saudi Arabia's majority Sunni population. Riyadh has taken a cautious but firm approach by arresting some protesters but releasing most of them quickly, and by using its state-sponsored clerics to counter political and Islamist activism. In addition, Saudi Arabia has seen protests among Shias in the Eastern Province, who have protested primarily against the detention of political prisoners, endemic discrimination, and Bahraini and Saudi Government actions in Bahrain. Protests are met by a strong police presence, with some arrests, but not the level of bloodshed seen in protests elsewhere in the region. In response to the unrest, King ABDALLAH in February and March 2011 announced a series of benefits for Saudi citizens including funds to build affordable housing, salary increases for government workers, and unemployment entitlements. To promote increased political participation, the government held elections nationwide in September 2011 for half the members of 285 municipal councils - a body that holds little influence in the Saudi Government. Also in September 2011, King ABDALLAH announced that women will be allowed to run for and vote in future municipal elections - first held in 2005 - and serve as full members of the advisory Consultative Council. The country remains a leading producer of oil and natural gas and holds about 16% of the world's proven oil reserves. The government continues to pursue economic reform and diversification, particularly since Saudi Arabia's accession to the WTO in 2005, and promotes foreign investment in the kingdom. A burgeoning population, aquifer depletion, and an economy largely dependent on petroleum output and prices are ongoing governmental concerns.