When the Ottomans left at the beginning of World War I, the British recognized Sheikh Abdullah bin Jassim Al Thani as ruler. The Al Thani family had lived in Qatar for 200 years. The 1916 treaty between the United Kingdom and Sheikh Abdullah was similar to those entered into by the British with other Gulf principalities. Under it, the ruler agreed not to dispose of any of his territory except to the U.K. and not to enter into relationships with any other foreign government without British consent. In return, the British promised to protect Qatar from all aggression by sea and to lend their good offices in case of a land attack. A 1934 treaty granted more extensive British protection.

In 1935, a 75-year oil concession was granted to the Qatar Petroleum Company, a subsidiary of the Iraq Petroleum Company, which was owned by Anglo-Dutch, French, and U.S. interests. High-quality oil was discovered in 1940 at Dukhan, on the western side of the Qatari peninsula. However, the start of WWII delayed exploitation of Qatar's oil resources, and oil exports did not begin until 1949.

During the 1950s and 1960s gradually increasing oil revenues brought prosperity, rapid immigration, substantial social progress, and the beginnings of Qatar's modern history. When the U.K. announced a policy in 1968 (reaffirmed in March 1971) of ending the treaty relationships with the Gulf sheikdoms, Qatar joined the other eight states then under British protection (the seven trucial sheikdoms--the present United Arab Emirates--and Bahrain) in a plan to form a union of Arab emirates. By mid-1971, as the termination date of the British treaty relationship (end of 1971) approached, the nine still had not agreed on terms of union. Accordingly, Qatar declared independence as a separate entity and became the fully independent State of Qatar on September 3, 1971.

In February 1972, the Heir Apparent, Sheikh Khalifa bin Hamad, deposed his cousin, Amir Ahmad, and assumed power. Key members of the Al Thani family supported this move, which took place without violence or signs of political unrest.