As airplanes first began to appear in warfare in the early years of the twentieth century, war's destruction suddenly extended beyond the battlefields to towns and cities. Increasingly, government leaders and the general public worried that enemy nations might bomb civilian populations. No organizations existed to protect civilian populations during wars, but in 1916, just before the United States entered World War I (1914–18), the U.S. government began to plan for home front defense. Congress created the Council of National Defense (CND), and the CND encouraged states to create state defense councils, which in turn encouraged creation of local defense councils.

World War II (1939–45) spurred much more extensive home front defense efforts; most of the defense strategies that were developed were built on the concept of civil defense. Civil defense refers to a system of defensive measures designed to protect civilians and their property from enemy attack...