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 geographically the largest sovereign state in the Middle East, the second-largest in the Arab world (after Algeria), the fifth-largest in Asia, and the 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. As of October 2018, the Saudi economy was the largest in the Middle East and the 18th largest in the world. Saudi Arabia also enjoys one of the world's youngest populations; 50% of its 33.4 million people are under 25 years old.
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 Fatimid (909–1171) caliphates as well as numerous other dynasties in Asia, Africa and Europe.