Wahhabi movement
The politico-religious Wahhabi movement had intervened in Yemen since 1803, and the area controlled by the imam had shrunk critically. Parts of the lowlands, Tihamah, stood under the chief of Abu Arish, Sharif Hamud, who took an independent position and sometimes supported the Wahhabi ruler. When Hamud died in 1818, he was succeeded by his son Ahmad. Ahmad allied with the Saudi family, leaders of the Wahhabi movement in order to fight Ottoman troops in Najd. However, the Ottoman forces were victorious and proceeded to invade Abu Arish. Ahmad was captured, and all his possessions in Yemen were returned to al-Mahdi Abdallah. In spite of mutual distrust, an agreement between the imam and the Ottomans was reached, whereby the imam sent coffee to the sultan's court. After 15 years, Tihamah was therefore once again in the hands of the Zaidi State.