The anticommunist crusade of the Federal Bureau of Investigation did not start with the Cold War. Based on research in the early files of the FBI's predecessor, the Bureau of Investigation, the author describes how the federal security officials played a decisive role in bringing about the first anticommunist hysteria in the US, the Red Scare in 1919 to 1920. The Bureau's political role, it is argued, originated in the attempt by the modern federal state during the early decades of the 20th century to regulate and control any organised opposition to the political, economic and social order.