During World War I, he was convinced that the Ottoman Empire, then the ruling power in Palestine, would fall and that in this vacuum the Jews could colonize Palestine if they had demonstrated service to the Allies. He thus convinced the British government to allow military participation by Jewish refugees from the Ottoman Empire.
In 1920 Jabotinsky organized and led a Jewish self-defense movement (Haganah) against the Arabs in Palestine. The British, who then ruled the country, sentenced him to 15 years at hard labour, but this action provoked such an outcry that he was soon reprieved. In the 1920s he was active in many international Zionist organizations, including the World Union of Zionist Revisionists in 1925.
Testifying before the British Royal Commission on Palestine, Jabotinsky gave an impassioned expression of his Revisionist views. The source of Jewish suffering was not merely anti-Semitism, he said, but the Diaspora (dispersion) itself; the Jews were a stateless people. Assigning cultural Zionism a relatively low priority, he advocated the creation of a Palestinian Jewish state on both sides of the Jordan, with continued Jewish immigration to achieve a Jewish majority there, and employment of Jewish troops for self-defense as part of the permanent garrison. In 1940, while in the United States to visit Betar, the youth organization of the Zionist Revisionist Party, Jabotinsky died of a heart attack. His followers, who had already founded theIrgun Zvai Leumi terrorist group, active in Palestine in the 1940s, later founded the Israeli Ḥerut Party.