Encoraged by the British, two sons of the Sharif Husayn Ibn 'Ali of the Hijaz, Faysal and Abdullah, rally their Hijaz tribesmen in open revolt against the Ottomans, opening another front in the Middle East that the Ottomans were unable to defend.
Assisted by British supplies, cash, and advisers (T E Lawrence -'Lawrence of Arabia' being one) Faysal's army then moves northward to Syria/Palestine, protecting the right flank of the British army of Allenby. Faysal enters Damascus in 1 October 1918, he formed a shortlived Arab government of Syria until the French elbow him out in 1920. Faysal pops up 12 months later as the British puppet king of Iraq.

With the Ikhwan in 1919, Ibn Saud strikes against the forces of Sharif Husayn. At Turabah they destroy Husayn's army, but instead of marching on Mecca, Ibn Saud is pressured by the British to keep out of Hijaz and to march on Hail instead. This infuriates the Ikhwan who for many years had harboured hatred of the Husayn family, and Hail for them had no religious significance. Between a rock and a hard place, Saud aquiesed to the British and turned his army northward taking Hail from the Rashidi Family in 1921.

Ibn Saud and the Ikhwan finally marched into Hijaz in 1924, captures At Ta'if, and occupied Mecca with no opposition, they then laid siege to both Jeddah and Medina. Both surrender by the end of 1925, and Hasayn -aided by the British, flees.

By 1927 the British had recognised Ibn Saud as a sovereign independant ruler, and several agreements later, Saudi Arabia's borders with the British mandates of Transjordan and Iraq are defined.