power. The British managed to occupy Aden and agreed to compensate the sultan with an annual payment of 6000 riyals. The British evicted the Sultan of Lahej from Aden and forced him to accept their "protection". In November 1839, 5000 tribesmen tried to retake the town but were repulsed and 200 were killed. The British realized that Aden's prosperity depended on their relations with the neighboring tribes, which required that they rest on a firm and satisfactory basis. 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 successor of Mohammed and the chief of the universal Caliphate. Ottoman return 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 Ottomans' 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; Yemenite Jews came to