From 1919 to 1920 the United States carried out a massive campaign against radicals, arresting and deporting thousands of radical immigrants in a matter of months, raiding and shutting down anarchist printing shops, and preventing anarchists from sending both periodicals and personal communications through the mail. This period is widely known as the First Red Scare, and is framed as a reaction to recent anarchist terrorism, syndicalist unionizing, and the Bolshevik Revolution. Though the 1919-20 First Red Scare was certainly unprecedented in its scope, it was made possible through a longer campaign against radicals, throughout which the US government constructed legal, ideological, and institutional apparatuses to combat radicalism and terrorism. This project explores the longer conflict between the US government and anarchists, focusing on the period between 1900 and 1920. It argues that the government sought to suppress radicalism not just due to anarchist terrorism or class antagonism, but also due to a broader ideology of antiradicalism that framed anarchist counterculture and connected ideas like free love and internationalism as a threat to the nation-state and to traditional American values. In trying to suppress radical counterculture years before the First Red Scare, the US government built its capacity for federal policing. And, by tying the battle against anarchist terrorism to a broader project of suppressing any idea considered to be radical or nontraditional, the US government controlled the kinds of ideas and people allowed within American borders through force, demarcating political limits to American nationality and citizenship.