Imam Yahya hamid ed-Din al-Mutawakkil was ruling the northern highlands independently from 1911. After the Ottoman departure in 1918, he sought to recapture the lands of his Qasimid ancestors. He dreamed of Greater Yemen stretching from Asir to Dhofar. These schemes brought him into conflict with the de facto rulers in the territories claimed, namely the Idrisids, Ibn Saud, and the British government in Aden. The Zaydi imam did not recognize the Anglo-Ottoman border agreement of 1905 on the grounds that it was made between two foreign powers occupying Yemen. The border treaty effectively divided Yemen into north and south. In 1915, the British signed a treaty with the Idrisids guaranteeing their security and independence if they would fight against the Turks. In 1919, Imam Yahya hamid ed-Din moved southward to “liberate” the nine British protectorates. The British responded by moving quickly towards Tihama and occupying al-Hudaydah. Then they handed it over to their Idrisi allies. Imam Yahya attacked the southern protectorates again in 1922. The British bombed Yahya’s tribal forces using aircraft to which the tribes had no effective counter.
In 1925, Imam Yahya captured al-Hudaydah from the Idrisids. He continued to follow and attack the Idrisids until Asir fell under the control of the imam’s forces, forcing the Idrisi to request an agreement that would enable them to administer the region in the name of the imam. Imam Yahya refused the offer on the grounds that the Idrisis were of Moroccan descent. According to Imam Yahya, the Idrisis, along with the British, were nothing but recent intruders and should be driven out of Yemen permanently. In 1927, Imam Yahya’s forces were about 50 km (30 mi) away from Aden, Taiz, and Ibb, and were bombed by the British for five days; the imam had to pull back. Small Bedouin forces, mainly from the Madh’hij confederation of Marib, attacked Shabwah but were bombed by the British and had to retreat.