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.