The Aden Protectorate ( ) was a British protectorate in South Arabia which evolved in the hinterland of the port of Aden and in the Hadhramaut following the conquest of Aden by the Bombay Presidency of British India in 1839, and it continued until the 1960s. In 1940 it was divided for administrative purposes into the Western Protectorate and the Eastern Protectorate. Today the territory forms part of the Republic of Yemen. The rulers of the Aden Protectorate, as generally with the other British protectorates and protected states, remained sovereign: their flags still flew over their government buildings, government was still carried out by them or in their names, and their states maintained a distinct 'international personality' in the eyes of international law, in contrast to states forming part of the British Empire, such as Aden Colony, where the British monarch was the head of state. History Informal beginnings What became known as the Aden Protectorate was initially informal arrangements of protection with nine tribes in the immediate hinterland of the port city of Aden: Abdali (Lahej) Alawi Amiri (Dhala) Aqrabi Aulaqi Fadhli Haushabi Subeihi Yafa British expansion into the area was designed to secure the important port that was, at the time, governed from British India. From 1874, these protection arrangements existed with the tacit acceptance of the Ottoman Empire that maintained suzerainty over Yemen to the north and the polities became known collectively as the "Nine Tribes" or the "Nine Cantons." Formal treaties of protection Beginning with a formal treaty of protection with the Mahra Sultanate of Qishn and Socotra in 1886, Britain embarked on a slow formalisation of protection arrangements that included over 30 major treaties of protection with the last signed only in 1954. These treaties, together with a number of other minor agreements, created the Aden Protectorate that extended well east of Aden to Hadhramaut and included all of the territory that would become South Yemen except for the immediate environs and port of the colonial capital, Aden. Aden with its harbour was the only area under full British sovereignty and, together with some offshore islands, was known as Aden Settlement (1839–1932), Aden Province (1932–1937), Aden Colony (1937–1963) and finally State of Aden (1963–1967). In exchange for British protection, the rulers of the constituent territories of the Protectorate agreed not to enter into treaties with or cede territory to any other foreign power. In 1917,