In 1918, the Jewish Legion, a group primarily of Zionist volunteers, assisted in the British conquest of Palestine. Arab opposition to British rule and Jewish immigration led to the 1920 Palestine riots and the formation of a Jewish militia known as the Haganah (meaning "The Defense" in Hebrew) in 1920 as an outgrowth of Hashomer, from which the Irgun and Lehi, or the Stern Gang, paramilitary groups later split off. In 1922, the League of Nations granted Britain the Mandate for Palestine under terms which included the Balfour Declaration with its promise to the Jews, and with similar provisions regarding the Arab Palestinians. The population of the area at this time was predominantly Arab and Muslim, with Jews accounting for about 11%, and Arab Christians about 9.5% of the population.