The Treaty of Darin, or the Darin Pact, of 1915 was between the United Kingdom and Abdul-Aziz Al Saud (sometimes called Ibn Saud) ruler of Emirate of Nejd and Hasa, who would go on to found the Kingdom of Saudi Arabia in 1932.
The Treaty was signed at Darin, on the island of Tarut on 26 December 1915 by Abdul-Aziz and Sir Percy Cox on behalf of the British Government.
The Treaty made the lands of the House of Saud a British protectorate and attempted to define its boundaries. The British aim of the treaty was to guarantee the sovereignty of Kuwait, Qatar and the Trucial States. Abdul-Aziz agreed not to attack British protectorates, but gave no undertaking that he would not attack the Sharif of Mecca
Also, he agreed to enter World War I in the Middle East against the Ottoman Empire as an ally of Britain.
The Treaty was the first to give international recognition to the fledgling Saudi state. Also, for the first time in Nejdi history the concept of negotiated borders had been introduced. Additionally, the British aim was to secure its Persian Gulf protectorates, but the treaty had the unintended consequence of legitimising Saudi control in the adjacent areas. The Treaty was superseded by the Treaty of Jeddah (1927).