In 1623, just two years after Native Americans and Pilgrims dined together at the first Thanksgiving, Pilgrim commander Myles Standish decapitated an enemy Indian chieftain and impaled his head on a pike outside of the Plymouth fort.
That's the part we typically omit from our Thanksgiving myth, which emphasizes interracial harmony instead of violence. And we certainly don't like to remember that our forefathers practiced beheading, especially when we're faced with an enemy that still engages in it.
After two American journalists were beheaded by Islamic State fighters, President Obama vowed to dismantle the organization, and has joined with five Arab allies to launch airstrikes on Islamic State targets.
But one of our allies, Saudi Arabia, still practices beheading. So does the Free Syrian Army, whom Obama pledged to assist in its battle to unseat dictator Bashar Assad. Unlike Assad's "extremist" foes, the argument goes, the Free Syrian Army is a "moderate" force. But it still beheaded six captives in September.
Indeed, beheading is as old as human civilization itself. So it also reminds us how close we remain to savagery, which is what makes decapitation so repulsive and alluring at the same time. We don't want to behold our own brutal natures. But we also can't look away, as the millions of YouTube hits illustrate.
The ancient Celts hung enemies' severed heads from horses' necks or nailed them to the front of their homes. The heads of important rival leaders were preserved in cedar oil and displayed to admiring guests.
To the conquering Romans, such rituals marked the Celts as uncivilized. But that gave the Romans license to behead Celts, who allegedly lay so far outside of human decency that its norms did not apply to them.
With the rise of nation-states, meanwhile, beheading became a force of political repression as well as revolution. As Scottish nationalists reminded voters in the recent failed referendum for independence, English monarchs routinely beheaded Irish and Scottish challengers to their rule. But in 1649, King Charles I was himself beheaded. By decapitating the sovereign head of state, the people proclaimed their own sovereignty.
That's also what happened in the French Revolution, of course, when Louis XVI and Marie Antoinette were both executed by a new beheading machine: the guillotine. Named after the French doctor who suggested it, the guillotine promised a more "humane" and efficient method of decapitation than the ax.
To horrified observers like England's Edmund Burke, however, the guillotine symbolized the brutality and instability that popular revolt unleashed. Marching in parades with their victims' heads on spikes, the French crowds reminded Burke of nothing so much as "a procession of American savages" — that is, of Native Americans — displaying enemy scalps.
By the late 1800s, as empires spread their reach, white Europeans and North Americans came to associate beheading almost exclusively with the racial or cultural "other." Never mind that Indians were themselves beheaded by whites, or that the French didn't outlaw the guillotine until 1977.
Americans continued to decapitate its foes too, using the same rationale as the Romans did: Some people are so savage that the rules of civilization don't apply to them. American troops decapitated a Japanese soldier in 1945 and propped his head on their tank for a picture. Troops did the same thing to an Iraqi soldier in 1991. But this time, Life magazine — which had declined to publish the World War II photo — put the new picture on its cover.
And the victim's eyes were pointed at us. Condemning Islamic State on Wednesday, President Obama said it "forces us to look into the heart of darkness." The allusion was to Joseph Conrad's classic 1899 novel, in which a deranged white colonist in Africa erects human heads on the fence around his house.
To Conrad, writing at the height of imperialism, the heads showed how whites could regress into the barbarism of the lesser races. Today, we know better — or we should. The savagery that you see on those YouTube videos isn't just in Islamic State, or in some other enemy that you fear and despise. It's in you too.
Jonathan Zimmerman is a professor of history and education at New York University. He is the author of "Too Hot to Handle: A Global History of Sex Education," which will be published next year by Princeton University Press.