The Balfour Declaration was a letter from foreign secretary Arthur Balfour to Anglo-Jewish Lord Walter Rothschild expressing British support for the creation of Jewish national home. Sent in November 1917, it gave official support to the Zionist movement, the wish to recreate a Jewish homeland in Palestine.
Historically, Jews had been the victims of widespread anti-Semitism, especially in Europe. They had no true home country, as former Israel was now predominantly Arab and under the control of foreign powers. Many high-ranking Jews in Britain started the Zionist movement, with the goal of creating a homeland for Jews in former Israel, away from discrimination and at times outright persecution in Europe. One of the movement's main leaders was Chaim Weizmann, a chemist from Russia, and he led talks with the British government.
The British government realized that supporting Zionism would in turn gain widespread Jewish support across Europe, perhaps helping win the war. After the war, Britain had administration over Palestine, and many Jews immigrated there throughout the 1920s, creating conflict with local Arabs and other non-Jews. However, the Jewish state of Israel would not be established until 1948.