This new book offers the first sustained history of Un-Americanism. Drawing on the extensive use of previously unused or underused archives, it argues that Un-Americanism has been a constant in American life from the Revolution to the Trump era, yet Americans have never agreed an objective definition for it. In 1945, for example, a Washington DC think tank was tasked by the House Un-American Activities Committee [HUAC] with defining the un-Americanism of its title, but despite considerable work was unable to do so; as late as 1957, the US Supreme Court Chief Justice declared that he had no idea what un-Americanism meant, how it could be defined or whether it ought ever to be investigated. American history can be understood as a series of contests, often between the political left and right, to become the public arbiter of un-Americanism’s meaning and therefore to control its boundaries and its use.

The book offers a series of thematic, chronologically arranged case studies that examine un-Americanism’s development. Starting with its origins in the Revolutionary period and its development in the nineteenth century, it examines: the American Legion’s attempts to be the first arbiter of un-Americanism’s meaning in the late 1910s, 1920s and 1930s; the creation of the first federal un-American investigative committee under Samuel Dickstein; the battles between Supreme Court and Congress  over who controlled the deployment of un-Americanism and its meanings in the 1940s and 1950s; the battle between southern segregationists and civil rights strategists to do the same in the 1950s and 1960s; and the creation of a coalition of liberal voices that eventually brought the downfall of HUAC in the 1960s and 1970s.