Young Israeli Girl

The Second Aliyah (1904–1914), began after the Kishinev pogrom; some 40,000 Jews settled in Palestine, but nearly half of them left. Both the first and second waves of migrants were mainly Orthodox Jews, but those in the Second Aliyah included socialist pioneers who established the kibbutz movement. During World War I, British Foreign Secretary Arthur Balfour issued what became known as the Balfour Declaration, which "viewed with favour the establishment in Palestine of a national home for the Jewish people". At the request of Edwin Samuel Montagu and Lord Curzon, a line was also inserted stating "it being clearly understood that nothing shall be done which may prejudice the civil and religious rights of existing non-Jewish communities in Palestine, or the rights and political status enjoyed by Jews in any other country".
The Jewish Legion, a group of battalions composed primarily of Zionist volunteers, assisted in the British conquest of Palestine. Arab opposition to the plan led to the 1920 Palestine riots and the formation of the Jewish organization known as the Haganah (meaning "The Defense" in Hebrew), from which the Irgun and Lehi paramilitary groups split off. In 1922, the League of Nations granted the United Kingdom a mandate over Palestine under terms similar to the Balfour Declaration. The population of the area at that time was predominantly Arab and Muslim, with Jews accounting for about 11% of the population.
The Third (1919–1923) and Fourth Aliyahs (1924–1929) brought an additional 100,000 Jews to Palestine. Finally, the rise of Nazism in the 1930s led to the Fifth Aliyah, with an influx of a quarter of a million Jews. This caused the Arab revolt of 1936–1939 and led the British to cap immigration with the White Paper of 1939. With countries around the world turning away Jewish refugees fleeing the Holocaust, a clandestine movement known as Aliyah Bet was organized to bring Jews to Palestine. By the end of World War II, the Jewish population of Palestine had increased to 33% of the total population.