And in every era, the same alarm bell has sounded.

In 1941, Vera Dean, the research director of the Foreign Policy Association, called for an “ideological offensive” against the Nazis. “It is not even enough for the British, with American aid, to carry out their war aims, which are to crush Hitlerism,” she said in a speech, “because the downfall or defeat of Hitler would not yet solve the political and economic and social problems that lie at the root of the present war.”

In 1943, Rabbi Barnett Brickner, a prominent figure in the U.S. military’s chaplain program, lamented that American troops were “muddled” about the war’s objectives. “This is a war of ideas, as well as weapons,” he said, and U.S. troops were at a “terrific disadvantage” against a “madly indoctrinated” enemy.

As it turned out, a muddled military force was rather up to the task of undermining Hitler’s ideology. The German leader’s narrative of Aryan ascendance was most clearly negated by Germany’s war defeat. Although Nazi sympathizers continue to exist, and still sometimes demonstrate alarming political strength, the conquest of Nazi Germany on the battlefield routed its ideology as well.

The Nazi example is particularly instructive when compared to the case of ISIS. Perhaps tens of thousands of Americans were sympathetic to Nazi ideology, including important national figures like Henry Ford and Charles Lindbergh, academic elites, and many more, even the residents of entire U.S. towns. In comparison, ISIS has recorded only trifling victories in the war of ideas. The FBI is currently pursuing hundreds of investigations into suspected ISIS supporters in the United States, and the group’s committed followers in the U.S. are likely in the very low thousands (when comparing this figure to the number of American Nazi sympathizers, keep in mind that the population of the United States has more than doubled since 1941). There are no ISIS towns in America. ISIS can claim no support from major celebrities or captains of industry in America or abroad. ISIS supporters are not invited to prestigious academic symposia—not in America and not in the Middle East.

When World War II ended, communism emerged as the new enemy in America’s ideas war. Institutions that had been created to fight Nazi ideology—such as the House Un-American Activities Committee and Voice of America—expanded to address this next challenge. Then, as now, social media was a component of the fight. In an annual “Letters From America Week” event, Americans gathered to lick stamps and write letters to friends and relatives abroad. “These letters may be written casually, about everyday affairs,” The New York Times reported at the time, “yet they carry, in their simple, sincere and direct way, a momentous message. For they tell nothing less than the story of America.”