In August 1775, when the Revolutionary War was still just a few months old, a private named William Simpson of Paxton Township, Pennsylvania, part of a battalion of volunteers from his state, arrived in Massachusetts to fight for the colonial cause against the British. But Simpson, who by one account was in his early 30s, never had a chance to do much fighting.

As detailed in a history of the unit, Simpson and his comrades had taken up a position on a hillside in Somerville, when they came under fire on the morning of August 27 from British artillery.

“Poor Simpson… had one of his legs shattered by a cannonball,” then-Lt. Col Edward Hand wrote in a letter a few days later.” Though a surgeon amputated Simpson’s mangled limb, the emergency operation wasn’t enough to save him. “The poor lad was buried this evening,” Hand reported.

Simpson was one of the 25,534 American combatants who lost their lives in the eight-year armed conflict, according to historian Howard H. Peckham’s 1974 book The Toll of Independence, widely regarded as the most accurate accounting of the death toll. But surprisingly, only about 27 percent of Americans actually died in battle, as Simpson did.

Musket, cannon balls and sabers weren’t as big of a threat to survival as diseases that spread through Continental Army camps and the prison ships that British forces used to confine American POWs.

Peckham, who meticulously gathered data on reports on 1,331 land engagements and 215 naval engagements, found that 8,624 American fighters were killed in battle. He also estimated that another 10,000 died in camp, and 8,500 perished while being held in captivity.

It’s unclear how many the British side lost, though the American Battlefield Trust, citing what it cautions is “unreliable imperial data,” puts the number of total British casualties—deaths, injuries, men who went missing in action or where captured—at 24,000. Approximately 7,500 Hessian mercenaries died in the war as well, according to the trust.

In raw numbers, the Revolutionary War’s death toll may not seem that high. The number of American military deaths in the Revolution is dwarfed by the total of 500,000 who died on the Union and Confederate sides in the Civil War, and is far smaller than the toll in World War I and World War II, the Korean War and the Vietnam War as well, according to U.S. Department of Veterans Affairs figures.

But because the population of the 13 colonies was only 2.5 million in 1776, the loss of 25,000 men had a big impact upon American society.

“About one percent of the population died in the war,” explains Michael Patrick Cullinane, a professor of history at Dickinson State University in North Dakota. “That would be the equivalent of losing three-and-a-half-million people in a war today.” The war’s toll left a shortage of young males to work on farms, in a new nation where agriculture was the dominant industry, he notes.

Military technology at the time of the Revolution was much more primitive than it is today, and the war was fought at a slower pace. But even without tanks, drones, high-powered rifles and night-vision goggles, historians say that the battlefield was plenty dangerous for soldiers.

“Firearms were a lot less accurate and the artillery was nowhere near as powerful,” explains Andrew Schocket, a professor in the history department at Bowling Green State University. “On the other hand, musket balls were huge and devastating compared to today’s much smaller-caliber bullets.”

The slowness and relative inaccuracy of 18th-century weapons also necessitated opposing soldiers getting close to one another. “With a musket from the Revolutionary War, you can only fire it two or maybe three times a minute, and you have to be within 100 to 300 yards to have a fighting chance of hitting the target,” explains Tyler Putman, an historian and senior manager of gallery interpretation at the Museum of the American Revolution in Philadelphia. That forced soldiers to stand in lines and coordinate their fire, which also made them easier targets.

While soldiers engaged in bayonet charges, being stabbed to death probably wasn’t as much of a risk as being shot, Putman explains. That’s because the charges’ real purpose was to frighten opponents, who often broke ranks and fled at the sight of bayonets.

When soldiers returned to camp after a battle, they were exposed to an environment that was arguably more dangerous than the battlefield, due to poor sanitation and soldiers’ vulnerability to infectious diseases. Early in the war, American forces were ravaged by smallpox, until Gen. George Washington in early 1777 began inoculating his soldiers against the disease. But other microbial threats persisted.

“Soldiers died of other diseases that we see in many other wars before modern sanitation, especially dysentery and typhus,” Schocket says.

Military physicians in the revolution “had no idea about germ theory, or about viral theory, or care for diseases,” Putman says. “They were very good at some things—amputation, for example, was a very professional and fast process. The problem is that they have no sense of what to do if you get an infection, or if you get dysentery. They don’t have the knowledge and the tools and the medicines that we do now to stave those things off.”

Being captured by the British in many cases proved to be a death sentence.

“Most of the enlisted men were held in prison ships, especially in the New York Harbor,” Schocket says. “The HMS Jersey was the most notorious.” He describes the floating prisons as “petri dishes of disease,” with captured Americans jammed below decks.

Worse yet, prisoners “were subject to the British military requisitioning system, which, at the time, was still largely privatized, in that officers were given a budget and often had the ability to keep what they saved. When it came to the choice of adequately feeding prisoners, or lining their own pockets by starving men they considered traitors, it was an easy choice for British officers.”

The trauma inflicted upon the young nation by the death toll in its fight for independence was a major influence upon the American identity, Cullinane theorizes.

“Because the death rate is so devastatingly high, we get the idea of American exceptionalism,” he says. While Americans don’t necessarily remember the deadliest battles, what has lasted is the idea of Americans having a distinctive will and tenacity to overcome their adversaries.