The Jewish Legion, a group primarily of Zionist volunteers, assisted, in 1918, 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), from which the Irgun and Lehi, or Stern Gang, paramilitary groups later split off. In 1922, the League of Nations granted Britain a mandate over 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 at about 9.5% of the population.