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."
In 1917, control of Aden Protectorate was transferred from the Government of India, which had inherited the British East India Company's interests in various princely states on the strategically important naval route from Europe to India, to the British Foreign Office. For administrative purposes, the protectorate was informally divided into the Eastern Protectorate (with its own Political Officer, a British advisor, stationed at Mukalla in Qu'aiti from 1937 to ca. 1967) and the Western Protectorate (with its own Political Officer, stationed at Lahej from 1 April 1937 to 1967), for some separation of administration.
The Eastern Protectorate (ca. 230,000 km²) came to include the following entities (mostly in Hadhramaut):
The Western Protectorate (ca. 55,000 km²) included:
The boundaries between these polities and even their number fluctuated over time. Some such as the Mahra Sultanate barely had any functioning administration. Not included in the protectorate were Aden Colony or the insular areas of Perim, Kamaran, and Khuriya Muriya that accrued to it.
Eastern Protectorate States
Western Protectorate States
These agreements allowed for the stationing of a Resident Advisor in the signatory states which gave the British a greater degree of control over their domestic affairs. This rationalized and stabilized the rulers’ status and laws of succession but had the effect of ossifying the leadership and encouraging official corruption. Aerial bombardment and collective punishment were sometimes used against wayward tribes to enforce the rule of Britain’s clients. British protection came to be seen as an impediment to progress, a view reinforced by the arrival of news of Arab nationalism from the outside world on newly available transistor radios.
In 1950, Kennedy Trevaskis, the Advisor for the Western Protectorate drew up a plan for the protectorate states to form two federations, corresponding to the two halves of the protectorate. Although little progress was made in bringing the plan to fruition, it was considered a provocation by Ahmad bin Yahya. In addition to his role as king, he also served as the imam of the ruling Zaidi branch of Shi'a Islam. He feared that a successful federation in the Shafi'i Sunnite protectorates would serve as a beacon for discontented Shafi'ites who inhabited the coastal regions of Yemen. To counter the threat, Ahmad stepped up Yemeni efforts to undermine British control and, in the mid-1950s, Yemen supported a number of revolts by disgruntled tribes against protectorate states. The appeal of Yemen was limited initially in the protectorate but a growing intimacy between Yemen and the popular Arab nationalist president of Egypt Gamal Abdel Nasser and the formation of United Arab States increased its attraction.