Saudi Arabia (, ; السعودية '), officially the Kingdom of Saudi Arabia (KSA; المملكة العربية السعودية ', ), is a country in Western Asia constituting the bulk of the Arabian Peninsula. With a land area of approximately, Saudi Arabia is the largest sovereign state in the Middle East, geographically the fifth-largest in Asia, second-largest in the Arab world after Algeria and 12th-largest in the world. Saudi Arabia is bordered by Jordan and Iraq to the north, Kuwait to the northeast, Qatar, Bahrain, and the United Arab Emirates to the east, Oman to the southeast and Yemen to the south. It is separated from Israel and Egypt by the Gulf of Aqaba. It is the only nation with both a Red Sea coast and a Persian Gulf coast, and most of its terrain consists of arid desert, lowland and mountains. Saudi Arabia is the largest by size, population and economy in the Middle East as of October 2018 and the 18th largest in the world.
The territory that now constitutes Saudi Arabia was the site of several ancient cultures and civilizations. The prehistory of Saudi Arabia shows some of the earliest traces of human activity in the world. The world's second-largest religion, Islam, emerged in modern-day Saudi Arabia. In the early 7th century, the Islamic prophet Muhammad united the population of Arabia and created a single Islamic religious polity. Following his death in 632, his followers rapidly expanded the territory under Muslim rule beyond Arabia, conquering huge and unprecedented swathes of territory (from the Iberian Peninsula in the West to modern day Pakistan in the East) in a matter of decades. Arab dynasties originating from modern-day Saudi Arabia founded the Rashidun (632–661), Umayyad (661–750), Abbasid (750–1517) and the Fatimid (909–1171) caliphates as well as numerous other dynasties in Asia, Africa and Europe.
The area of modern-day Saudi Arabia formerly consisted of mainly four distinct regions: Hejaz, Najd and parts of Eastern Arabia (Al-Ahsa) and Southern Arabia ('Asir). The Kingdom of Saudi Arabia was founded in 1932 by Ibn Saud. He united the four regions into a single state through a series of conquests beginning in 1902 with the capture of Riyadh, the ancestral home of his family, the House of Saud. Saudi Arabia has since been an absolute monarchy, effectively a hereditary dictatorship governed along Islamist lines. The ultraconservative Wahhabi religious movement within Sunni Islam has been called "the predominant feature of Saudi culture", with its global spread largely financed by the oil and gas trade. Saudi Arabia is sometimes called "the Land of the Two Holy Mosques" in reference to Al-Masjid al-Haram (in Mecca) and Al-Masjid an-Nabawi (in Medina), the two holiest places in Islam. As of 2013, the state had a total population of 28.7 million, of which 20 million were Saudi nationals and 8 million were foreigners. As of 2017, the population is 33 million. The state's official language is Arabic.
Petroleum was discovered on 3 March 1938 and followed up by several other finds in the Eastern Province. Saudi Arabia has since become the world's second largest oil producer behind the U.S. and exporter, controlling the world's second largest oil reserves and the sixth largest gas reserves. The kingdom is categorized as a World Bank high-income economy with a high Human Development Index and is the only Arab country to be part of the G-20 major economies. The state has attracted criticism for its treatment of women and use of capital punishment. Saudi Arabia is an autocratic monarchy, has the third-highest military expenditure in the world and SIPRI found that Saudi Arabia was the world's second largest arms importer in 2010–2014. Saudi Arabia is considered a regional and middle power. In addition to the GCC, it is an active member of the Organisation of Islamic Cooperation and OPEC.