In the next 4 years, the Saudi ruler was preoccupied with consolidation of his domain, undertaking several campaigns in new regions of Arabia, while keeping the Hejazi frontier quiet. Jabal Shammar was annexed in 1920-21, while Kuwait was defeated in 1922, defining the border with Iraq and Transjordan through the Uqair protocol of 1922, while simultaneously conquering Asir in south Arabia. By early 1923, Ibn Saud decided to take over Hejaz, but was unsure over British position. The worsening relations between England and Hashemite rulers and the proclamation of Sharif Husayn as Caliph, finally made Ibn Saud to undertake the campaign, entusiasthically supported by the religiously insigted Ikhwan, who had hoped to take over the holy sites of Islam. The preliminary attack on Taif came in September 1924, beginning the Saudi conquest, which would be complete on December 1925.
Question: What was the last Saudi conquest?
Answer: take over Hejaz