“internal security”

required the registration of communist organizations in the United States and established the Subversive Activities Control Board to investigate persons thought to be engaged in “un-American” activities. It was a key institution in the era of the Cold War, tightening alien exclusion and deportation laws and allowing for the detention of dangerous, disloyal, or subversive persons in times of war or “internal security emergency.” Most of its provisions were later declared unconstitutional.