The first wave of modern Jewish migration to Ottoman-ruled Palestine, known as the First Aliyah, began in 1881, as Jews fled pogroms in Eastern Europe.
The Second Aliyah (1904–14), began after the Kishinev pogrom; some 40,000 Jews settled in Palestine, although nearly half of them left at a later point in time.
Both the first and second waves of migrants were mainly Orthodox Jews, although the Second Aliyah included socialist groups who established the kibbutz movement.
During World War I, British Foreign Secretary Arthur Balfour sent a letter that stated:
His Majesty’s government view with favour the establishment in Palestine of a national home for the Jewish people, and will use their best endeavours to facilitate the achievement of this object, 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 primarily of Zionist volunteers, assisted in the British conquest of Palestine in 1917. 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 similar to the Balfour Declaration.
The population of the area at this time was predominantly Arab and Muslim, with Jews accounting for about 11%.