After the 1920 Arab riots and 1921 Jaffa riots, the Jewish leadership in Palestine believed that the British (whom the League of Nations had given a mandate over Palestine in 1920 for the purpose of establishing a Jewish national home) had no desire to confront local Arab gangs over their attacks on Palestinian Jews. Realizing that they could not rely on the British administration for protection from these gangs, the Jewish leadership created the Haganah to protect their farms and Kibbutzim. In addition to guarding Jewish communities, the role of the Haganah was to warn the residents of and repel attacks by Palestinian Arabs. In the period between 1920–1929, the Haganah lacked a strong central authority or coordination. Haganah "units" were very localized and poorly armed: they consisted mainly of Jewish farmers who took turns guarding their farms or their kibbutzim. Following the Arab massacres of 1929, the Haganah's role changed dramatically. It became a much larger organization encompassing nearly all the youth and adults in the Jewish settlements, as well as thousands of members from the cities. It also acquired foreign arms and began to develop workshops to create hand grenades and simple military equipment, transforming from an untrained militia to a capable underground army.