years. The trucial system received formal permanency with the "1853 Treaty of Maritime Peace in Perpetuity." The British policy of non-involvement in the internal affairs of the Trucial sheikhs was abandoned with passage of the "Exclusive Agreement" in March 1892. This agreement prohibited the Trucial rulers from yielding territorial sovereignty without British consent. Britain, moreover, assumed responsibility for foreign relations and thus, by implication, their protection. This treaty marked Britain's shift from commercial to strategic priorities and formed the diplomatic pillar of British authority in the Trucial states. Post World War I In the years following World War I, the Trucial sheikhs found their capacity to act independently being continuously curtailed by the British. This was partially a result of Britain shifting attention away from Iran, where Reza Shah's nationalist assertion of power undercut their hegemony. It also reflected growing commercial and imperial communications interests, such as air route facilities. For example, according to agreements concluded in February 1922, the Trucial sheikhs pledged themselves not to allow the exploitation of oil resources in their territories except by "persons appointed by the British government". Even more restrictive was the ultimatum issued by the political resident in 1937 requiring Trucial states to do business exclusively with Petroleum Concessions Ltd., a wholly owned subsidiary of the London-based Iraq Petroleum Company, which was itself partly owned by the Anglo-Iranian Oil Company (AIOC). Instead of reflecting higher demand for oil (England then had adequate supply), this ultimatum was designed to block other parties out of the economic and political affairs of the Trucial States. In 1946, the Persian Gulf residency left its location in Bushehr and relocated to a new base in Bahrain. However, while Reza Shah succeeded in removing Britain from Iranian territory, his efforts to curtail their role in the Iranian oil industry backfired, and led to an extension of the concession operated by the British government-owned Anglo-Iranian Oil Company. From their new base in Bahrain, the British resident directed other political agents in Bahrain, Kuwait, Qatar and Oman until those regions became independent. Duties of the Residency On 1 April 1947, the British political residency came under the authority of the Foreign Office, 'graded' as an ambassador in the Persian Gulf. The political resident accomplished his obligations by using a network of representatives known as political agents, operating in Bahrain, Qatar, Dubai and Abu Dhabi. Additionally, political officers were retained for the