Italy entered World War II in June 1940, as part of the Axis, alongside Germany. General Maitland Wilson, Commander of the British forces in Egypt, formally asked Sayyid Idris to establish a Senussi force to fight the Italians alongside the British. Once a group of Tripolitanians had joined forces with the Cyrenaicans, the Senussi force became the Libyan Arab Force.

The Libyan Arab Force took part in the Western Desert Campaign, and were thanked publicly by British Foreign Secretary Anthony Eden in the House of Commons in January 1942:

“The Sayyid Idris al-Senussi made contact with the British authorities in Egypt within a month of the collapse of France, at a time when the military situation in Africa was most unfavourable to us. A Senussi force was subsequently raised from those of his followers who had escaped from Italian oppression at various times during the past twenty years. The force performed considerable ancillary duties during the successful fighting in the Western Desert in the Winter of 1940-41, and is again playing a useful part in the campaign now in progress. I take this opportunity to express the warm appreciation of His Majesty’s Government for the contributions which Sayyid Idris al-Senussi and his followers have made and are making to the British war effort. We welcome their association with His Majesty’s forces in the task of defeating the common enemies. His Majesty’s Government is determined that at the end of the war the Senussi in Cyrenaica will in no circumstances again fall under Italian domination”.

Despite the British guarantee that Cyrenaica would never fall to the Italians, Sayyid Idris and the Tripolitanian leaders were disappointed that Eden had not promised Libyan independence. Indeed, after the war Libya’s future was unclear: the international community was concerned that it was not ready for independence. In 1951, when the newly formed United Kingdom of Libya became independent, the UN helped to organise civil administration. Britain and the US chiefly funded this work.

In 1953 Britain formalised its relations with Libya under the Anglo-Libyan treaty of friendship and alliance. This treaty gave Great Britain facilities for military purposes (such as public land, and transport infrastructure) in exchange for aid. The aid included balancing the state budget, as well as constructing infrastructure such as roads, water and power works, schools, universities and hospitals. The treaty was intended to last for twenty years, with a rate of $10,500,000 for the first five years. The treaty nearly lasted its full remit; Libya terminated the treaty in January 1972.