The British government concluded “protection and friendship” treaties with nine tribes surrounding Aden, whereas they would remain independent from British interference in their affairs as long as they do not conclude treaties with foreigners (non-Arab colonial powers). Aden was declared a free zone in 1850. With emigrants from India, East Africa, and Southeast Asia, Aden grew into a world city. In 1850, only 980 Arabs were registered as original inhabitants of the city. The English presence in Aden put them at odds with the Ottomans. The Turks asserted to the British that they held sovereignty over the whole of Arabia, including Yemen as the successor of Mohammed and the Chief of the Universal Caliphate.
The Ottomans were concerned about the British expansion from India to the Red Sea and Arabia. They returned to the Tihama in 1849 after an absence of two centuries. Rivalries and disturbances continued among the Zaydi imams, between them and their deputies, with the ulema, with the heads of tribes, as well as with those who belonged to other sects. Some citizens of Sana’a were desperate to return law and order to Yemen and asked the Ottoman Pasha in Tihama to pacify the country. Yemeni merchants knew that the return of the Ottomans would improve their trade, for the Ottomans would become their customers. An Ottoman expedition force tried to capture Sana’a, but was defeated and had to evacuate the highlands. The Opening of the Suez Canal in 1869, strengthened the Ottoman decision to remain in Yemen. In 1872, military forces were dispatched from Constantinople and moved beyond the Ottoman stronghold in the lowlands (Tihama) to conquer Sana’a. By 1873, the Ottomans succeeded in conquering the northern highlands. Sana’a became the administrative capital of Yemen Vilayet.
The Ottomans learned from their previous experience and worked on the disempowerment of local lords in the highland regions. They even attempted to secularize the Yemeni society, while Yemenite Jews came to perceive themselves in Yemeni nationalist terms. The Ottomans appeased the tribes by forgiving their rebellious chiefs and appointing them to administrative posts. They introduced a series of reforms to enhance the country’s economic welfare. However, corruption was widespread in the Ottoman administration in Yemen. This was because only the worst of the officials were appointed because those who could avoid serving in Yemen did so. The Ottomans had reasserted control over the highlands for a temporary duration. The so-called Tanzimat reforms were considered heretic by the Zaydi tribes. In 1876, the Hashid and Bakil tribes rebelled against the Ottomans; the Turks had to appease them with gifts to end the uprising.
The tribal chiefs were difficult to appease and an endless cycle of violence curbed Ottoman efforts to pacify the land. Ahmed Izzet Pasha proposed that the Ottoman army evacuate the highlands and confine itself to Tihama, and not unnecessarily burden itself with continuing military operation against the Zaydi tribes. The hit-and-run tactics of the northern highlands tribesmen wore out the Ottoman military. They resented the Turkish Tanzimat and defied all attempts to impose a central government upon them. The northern tribes united under the leadership of the House of Hamidaddin in 1890. Imam Yahya Hamidaddin led a rebellion against the Turks in 1904; the rebels disrupted the Ottoman ability to govern. The revolts between 1904 and 1911 were especially damaging to the Ottomans, costing them as many as 10,000 soldiers and as much as 500,000 pounds per year. The Ottomans signed a treaty with imam Yahya Hamidaddin in 1911. Under the treaty, Imam Yahya was recognized as an autonomous leader of the Zaydi northern highlands. The Ottomans continued to rule Shafi’i areas in the mid-south until their departure in 1918.