Born in Russia, he became a British citizen in 1910. A supporter of Zionism from the early 1900s, Weizmann participated in the negotiations that led to the Balfour Declaration (1917), which outlined British support for a Jewish homeland in Palestine. He later served as President of the World Zionist Organization (1920–31; 1935–46), facilitating Jewish immigration into Palestine in the 1930s. Weizmann also played an important role in persuading the US government to recognize the new state of Israel (1948) and became its first President in 1949.