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
massacres of 1929
1929 Palestine riots
Jewish military history