A U.S. flag stands next to the grave marker of U.S. Army Staff Sergeant Ayman Taha inside of Section 60 in Arlington National Cemetery on Memorial Day, May 30, 2016. REUTERS

President Donald Trump drew bipartisan criticism when he defended Vladimir Putin against charges the Russian president was a killer, telling Bill O'Reilly Sunday, "We've got a lot of killers. What, do you think our country's so innocent?"

Democrats and Republicans condemned Trump's remarks. But while critics attacked the president for drawing what they called a "moral equivalency" between the U.S. and Putin's Russia, what Trump said is unavoidably true: especially when it comes to war, America kills.

So just how many foreigners has America killed over the course of its history? It’s a tricky question to answer. While the U.S. does a good job of tracking American casualties, it doesn’t do quite as well tallying up the casualties it incurs on its enemies. By using a variety of estimates, we can get a general sense of the number of lives the U.S. has taken during major military operations over the course of its history.

The American Revolution (1775-1783): British forces suffered 24,000 casualties, according to Campaign 1776, a non-profit dedicated to preserving U.S. battlefields. Another 1,200 Hessians -- German mercenaries hired by the British -- were killed in battle.

Indian Wars: In 1894, the U.S. government attempted to tally the total number of American Indians killed in battle with the U.S. army. Over the course of 40 Indian Wars, U.S. forces tallied 30,000 American Indians killed, while admitting the actual number was probably much higher.

"The number... is of those found by the whites," a 1894 government report said. "Fifty percent additional would be a safe estimate to add to the numbers given."

That would put the numbers at 45,000, although that number doesn't include the many lives lost to government policies. Early census records don’t include American Indians, so it’s hard to know for sure how the Native population in the U.S. declined over the course of American history. There isn’t even much agreement on what the entire pre-Columbian population of the entire Americas was -- estimates range from a few million to more than 100 million. What is known is that less than 300,000 Native Americans lived in the U.S. in 1900.

Beyond just the fighting in “Indian Wars,” U.S. policies contributed to the deaths of thousands and thousands of natives. For example, it is estimated that 4,000 Cherokee died from cold, hunger and disease on the "Trail of Tears."

War of 1812 (1812-1815): Combined British and Canadian casualties have been estimated to be 8,600. While Native Americans played a major role in the war, no reliable records exist to determine their casualties.

Mexican-American War (1846-1848): Incomplete estimates by the Mexican government put total Mexican casualties at 25,000, according to historian Kennedy Hickman.

American Civil War (1861-1865): Total casualties during the war between the states tops one million, with 642,427 Union casualties and 483,026 Confederate casualties, according to the National Park Service.

Spanish-American War (1898): Spanish Navy casualties were between 860 and 960 and major land battles led to the death of 215 soldiers and another 376 wounded, according to Donald Dyal's "Historical Dictionary of the Spanish-American War." Most deaths in this war were caused by disease: Dyal estimates that for every combat casualty there were 10 casualties caused by illness.

Philippine-American War (1899-1902): In perhaps the least known conflict in American history, U.S. forces killed over 20,000 Filipino combatants after taking control of the Philippines from the Spanish in the aftermath of the Spanish-American war. Another 200,000 Filipino civilians died from "violence, famine and disease," according to the U.S. State Department.

World War I (U.S. involvement spanned 1917-1918): The Central Powers suffered 3 to 4.5 million military deaths in the Great War, but the U.S began fighting three years into the war, so the majority of the those casualties were probably inflicted by U.S. allies before the U.S joined the fight.

World War II (U.S involvement spanned 1941-1945): The U.S. entered the the Second World War two years into the conflict. Fighting on two fronts, the U.S. delivered large casualties to the Axis powers. According to the National World War II Museum, Germany suffered 5.5 million military deaths, and another 6.6 to 8.8 million civilian deaths during the course of the war. Battling the U.S. in the Pacific, Japan lost 2.1 million solders and suffered another 2.6 to 3.1 million civilian deaths. The U.S. also fought in Italy, which lost more than 700,000 civilians and military personnel.

With World War II, the relationship between war and the dead changed significantly. With the advent of strategic bombing campaigns and the sieging of population centers, more civilians than soldiers were dying in military conflicts.

As the Cold War began, growing global intelligence services and the possibility of proxy wars meant the the U.S. could cause deaths without deploying large armies. The relationship between the U.S. military and the casualties it caused became more complicated. For example, is the U.S. responsible for the deaths caused by countries it arms?

The Centre for Research on Globalization tried to understand just how many deaths the U.S. was responsible for since the end of World War II. It counted conflicts in which the U.S. "appeared to have been a necessary cause of a war or conflict" and attributed casualties in those conflicts to the U.S. Using that criteria, the Centre said the U.S. was responsible for 20 million deaths across 37 victim nations, including Afghanistan, Cuba, the Dominican Republic, Iraq, North and South Korea, Yugoslavia and Vietnam since 1945.