In 1902, Abdul-Aziz Al Saud, leader of the Al Saud, returned from exile in Kuwait and began a series of conquests, starting with the seizure of Riyadh from the Al Rashid. These conquests laid the foundation for the Third Saudi State and ultimately the modern state of Saudi Arabia, established in 1930. The Ikhwan, a Wahhabist-Bedouin tribal army led by Sultan bin Bajad Al-Otaibi and Faisal al-Duwaish, was instrumental in these conquests.^[28]

By 1906, Abdulaziz had expelled the Al Rashid from Najd, gaining recognition as an Ottoman client. In 1913, he captured Al-Hasa from the Ottomans, acquiring control of the Persian Gulf coast and future oil reserves. Abdulaziz avoided the Arab Revolt, recognizing Ottoman suzerainty in 1914, and focused on defeating the Al Rashid in northern Arabia. By 1920, the Ikhwan had seized Asir in the southwest, and in 1921, Abdulaziz annexed northern Arabia after defeating the Al Rashid.^[29]

Abdulaziz initially avoided invading the Hejaz, protected by Britain. However, in 1923, with British support withdrawn, he targeted the Hejaz, leading to its conquest by the end of 1925. In January 1926, Abdulaziz declared himself King of the Hejaz, and in January 1927, King of Najd. The Ikhwan's role in these conquests significantly altered the Hejaz, imposing Wahhabi culture.^[30]

The Treaty of Jeddah in May 1927 recognized the independence of Abdul-Aziz's realm, then known as the Kingdom of Hejaz and Najd.^[29] After the Hejaz conquest, the Ikhwan sought to expand into British territories but were halted by Abdulaziz. The resulting Ikhwan revolt was crushed at the Battle of Sabilla in 1929.^[31]

In 1932, the Kingdoms of Hejaz and Najd united to form the Kingdom of Saudi Arabia.^[28] Boundaries with neighboring states were established through treaties in the 1920s, and the southern boundary with Yemen was defined by the 1934 Treaty of Ta'if after a brief border conflict.^[32]