Part of American Exceptionalism is never having to admit when your government kills hundreds of thousands of people.

A new study says the U.S. invasion and subsequent war in Iraq killed an estimated 460,800, higher than most of the estimates frequently cited in the mainstream media, but lower than the controversial 2006 Lancet study that estimated between 400,000 and 655,000 excess deaths.

The authors of the study, which was published in PLOS Medicine, detail a more rigorous methodology than has ever been employed for previous Iraq War mortality estimates.

But even this may be an undercount. John Tirman, Executive Director at the MIT Center for International Studies and author of The Deaths of Others, told me in an email that the new study’s estimate of deaths of displaced people, approximately 56,000, is “likely to be more like 100,000 or even greater, but it’s almost impossible to say without more research—i.e., a survey among the displaced.”

Whatever the exact number, what’s certain is that it continues to grow. According to the International Crisis Group, the violence in Iraq is “as acute and explosive as ever.” And as Antiwar.com’s own Kelley Vlahos wrote recently, Iraqis are dying in “numbers not seen since the bloody days of 2008.”

Unfortunately, Americans dramatically under-estimate how many Iraqis died as a result of their former president’s war of choice.

“While even the most conservative estimates of mortality in Iraq,” Al Jazeera America reports, “have reached six figures, polling in the U.S. (PDF) and U.K. (PDF) have shown public perception to be that the civilian death toll from the war is in the neighborhood of 10,000.”

That is an embarrassment of enormous magnitude. But one is careful not to be surprised. Back in 2011, a University of Maryland poll found that 38 percent of Americans still believe the U.S. had “found clear evidence in Iraq that Saddam Hussein was working closely with the al-Qaeda terrorist organization.”

So not only do Americans refuse to accept the reality of why the U.S. attacked Iraq, but they resist the facts about the consequences of the war. The notion that we went to war on false pretenses and that it directly led to the deaths of about 500,000 people is too much to bear for flag-waving Americans.

If their ignorance weren’t so offensive, it might be excusable. The reality is that a group of people that the American electorate twice empowered at the voting booths made decisions to act criminally and killed hundreds of thousands of people needlessly by attacking and occupying a country that posed no threat to us. They get away with this mass murder, in part, because of the mass ignorance of Americans.

A death count statistic can never truly depict the unimaginable suffering caused by the U.S. in Iraq. But the 10,000 civilians America believes were killed by the war is not an acceptable representation of the ~500,000 Iraqis that actually died and the millions that had their lives torn apart.

I shudder to think how many Americans know that more than 6,000 Iraqi civilians have been killed in 2013, two years after the U.S. withdrawal.