Saudi Arabia, officially the Kingdom of Saudi Arabia, is a Western Asian nation that occupies the majority of the Arabian Peninsula. Saudi Arabia is the largest sovereign state in Western Asia, the second-largest in the Arab world, the fifth-largest in Asia, and the 12th-largest in the world, with a land area of approximately 2,150,000 km2. 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; the Gulf of Aqaba separates Saudi Arabia from Egypt and Israel to the north-west. Saudi Arabia is the only country in the world with coasts on both the Red Sea and the Persian Gulf, and its landscape is mostly made up of arid desert, lowland, steppe, and mountains. Saudi Arabia's economy was the largest in the Middle East and the 18th largest in the world as of October 2018. Saudi Arabia also has one of the world's youngest populations, with about half of its 34.2 million people under the age of 25. The land that now makes up Saudi Arabia was once home to a number of ancient cultures and civilizations. Saudi Arabia's prehistory contains some of the world's earliest evidence of human activity. Modern-day Saudi Arabia is the birthplace of Islam, the world's second-largest religion. The Islamic prophet Muhammad brought the people of Arabia together and established a single Islamic religious polity in the early seventh century. Following his death in 632, his followers quickly spread Muslim rule beyond Arabia, capturing vast and unparalleled swaths of land in a matter of decades. The Rashidun, Umayyad, Abbasid, and Fatimid caliphates, as well as various other dynasties in Asia, Africa, and Europe, were established by Arab dynasties originating in modern-day Saudi Arabia. The area of modern-day Saudi Arabia was previously divided into four distinct historical regions: Hejaz, Najd, parts of Eastern Arabia, and Southern Arabia. King Abdulaziz founded the Kingdom of Saudi Arabia in 1932. Through a series of conquests, he unified the four regions into a single state, starting in 1902 with the capture of Riyadh, the ancestral home of his ancestors, the House of Saud. Since then, Saudi Arabia has become a authoritarian absolute monarchy ruled by an Islamist hereditary dictatorship. The Wahhabi religious movement within Sunni Islam has been dubbed "the dominant characteristic of Saudi culture," with its global expansion largely funded by the oil and gas trade. The two holiest mosques in Islam, Al-Masjid al-Haram and Al-Masjid an-Nabawi, are often referred to as "the Land of the Two Holy Mosques." Arabic is the state's official language. On March 3, 1938, petroleum was found, followed by several other discoveries in the Eastern Province.