Until the founding of the State of Israel in 1948, the years 1914-1921 constituted the high point of Zionism in America. Two factors were responsible: the outbreak of World War I which shifted major Zionist responsibility to the United States, and the assumption of the leadership of the American Zionist movement by Progressive reformer Louis D. Brandeis. Under Brandeis' Chairmanship the American Zionist organization changed, developing emphases and goals different from the Zionists in Europe. Responding to intellectual formulations rather than to the pressures of felt antisemitism, Brandeis-led Zionism rejected the traditional Zionist definition of Palestine as an asylum for the oppressed and adopted, instead, the goal of a Jewish nation that would serve as a model social democracy. In tune with the prevailing Progressive emphasis on efficiency and on scientific management, but in contrast to the relaxed and informal operations of the European Zionists, Brandeis stressed organizational discipline and order. Unlike the Europeans, who formed distinct groups of "practical" or "spiritual" Zionists, the American Zionists combined the two; they were "Messianic pragmatists" who defined a Utopian vision for the Jewish people, and then set out, by the most practical means possible, to achieve it. Much of the American definition of Zionism during this period came from an almost anonymous individual, social philosopher Horace M. Kallen, who acted behind the scenes in many capacities. From 1914 until 1921, when a major dispute Letween the American Zionist leaders and their European counterparts over their differing conceptions of Zionism forced Brandeis and Kallen to leave the Zionist movement, Brandeis relied on Kallen in many ways. Kallen, a fellow Progressive, helped to formulate and to implement plans for efficient reform of the organization; he originated many of the ideas that Brandeis and others used as a basis for action in the Jewish community; he became a "missionary" trying to convert both Jews and non-Jews to the Zionist cause; he was, for quite some time, the sole American link with important Zionist activity in Great Britain; he prepared the outlines which American Zionists viewed as basic to the reconstruction of Palestine. Because Kallen did so much for American Zionism during this period, and because his approach to Zionism was influenced both by the philosophy of Pragmatism and the values of Progressivism, a presentation and analysis of his correspondence and records of those years does more than delineate the roles Kallen played as a Zionist activist. It presents, also, a picture of the Zionist movement in America during a crucial decade, showing the way the organization took on an American cast, and relating the development of this Americanized Zionist organization to the mood and values of the dominant American culture of the period.