In the 1930s and 1940s, the rise of Nazism forced American liberals to defend their political beliefs, especially during World War II. This was followed by the reemergence of Soviet Communism as a threat to American liberalism when the Cold War began in the late 1940s. As American thinkers struggled against these ideological enemies, they were forced to explicitly describe liberal political and legal theory, unleashing a clash of ideas over what an ideal political order should look like.American liberals deployed a defensive strategy that criticized the opponents of liberalism, aligning Nazism and Communism together under the framework of “totalitarianism” as an example of what liberalism was not. At the same time, American liberals grappled with the more difficult task of building a positive political philosophy that explained what precisely defined a liberal political order and how it ought to be organized – analyzing the centrality of individual rights, the role of democracy, the importance of international law, and the relationship between capitalism and government in a liberal society. German émigrés to the United States in the 1930s played an important role in defining and defending American liberalism. After escaping the Nazis, a small group of émigrés coalesced in the early 1940s around the American lawyer David Riesman – who later became a leading American social theorist in the 1950s. The most influential members of this “Riesman club” included the political theorist Carl J. Friedrich – Riesman’s mentor from Harvard – and several Frankfurt School scholars, including the lawyer and political theorist Franz Neumann and the psychoanalyst Erich Fromm – another Riesman mentor. The group also included émigré lawyers Otto Kirchheimer and Ernst Fraenkel. The German émigrés Neumann and Friedrich, and the American Riesman, became influential in the U.S. as they sought to explain and protect the ideas underpinning American liberalism from the 1930s to the early 1960s. During the 1930s and 1940s, Neumann analyzed how antitrust law could be used to battle Nazism. After World War II, he worked with Telford Taylor, a U.S. prosecutor at the Nuremberg Trials, to develop a comprehensive study of how these trials changed international law. Friedrich sought to create a new theory of democracy, influenced by the German jurist Otto von Gierke, that Americans could use to fight totalitarianism. And Riesman crafted a theory of utopian liberalism that he believed could invigorate politics in the U.S. by better attuning liberalism to Americans’ deepest desires. Some refugees from Europe, especially the neo-liberal Austrian émigré Friedrich Hayek, argued that liberalism was synonymous with individualism. In contrast, Neumann, Friedrich, and Riesman asserted that liberalism required an interwoven relationship between the need for social cooperation and the individual desire for personal autonomy. This form of American liberalism could be called solidaristic liberalism. Solidaristic liberals believed the Nazis and Soviets provided examples of societies with uncritical obsequiousness toward government coordination. At the same time, solidaristic liberals sought to avoid the atomism of neo-liberalism by emphasizing the importance of empathy between citizens and loyalty to various cultural groups in a diverse, pluralistic state.