Centuries before the arrival of Europeans, Indigenous people in the Western United States learned how to live with fire. They knew the recipe for catastrophic seasonal wildfires—bone-dry grasses, fallen logs and other forest debris, and high winds—and took measures to protect old-growth stands of trees.

In many cases, those methods involved using fire to prevent fire. In the late winter and spring, when conditions were cooler and wetter, Native people would light controlled fires to burn up available fuel that could trigger a far more destructive, late-summer wildfire.

“There's cultural burning, there's prescribed burning, there's light burning,” says William Deverell, a historian of the American West at the University of Southern California. “The goal in terms of fire mitigation is all the same. Let's see if we can mitigate the fuel load.”

When the U.S. Forest Service was founded in 1905, there was growing interest in traditional “controlled burning” practices, which were already being used by some non-Native farmers and ranchers. But that all changed in August of 1910, when a historic wildfire engulfed three Western states and killed 87 people. In the wake of that epic conflagration, the Forest Service took a hardline stance that dominated America’s fire-prevention efforts for nearly a century: no fire is a good fire.

The Great Fire of 1910—also known as the “Big Burn” or the “Big Blow Up”—is still the largest single wildfire in American history. More than 3 million acres of forest burned across the states of Montana, Idaho and Washington.

“We’re talking about a gargantuan swath of land,” says Deverell, “just a huge section of the Northern Plains and Mountain West region of the United States.”

The intensity of the Great Fire was also unprecedented. On August 20, dozens of small wildfires in drought-stricken Idaho and Montana were whipped into a frenzy by 70-mph winds. Tornado-like plumes of flame raced across the treetops.

“The forests staggered, rocked, exploded and then shriveled under the holocaust,” wrote Betty Goodwin Spencer, an Idaho writer who witnessed the fire. “Great red balls of fire rolled up the mountainsides.”

The U.S. Forest Service, which had only been operational for five years, did everything it could to control the blaze, deploying 4,000 soldiers to assist thousands of firefighters on the ground. Entire towns like Wallace, Idaho were leveled by the wildfire and 87 people died, including 78 firefighters. Smoke from the Great Fire darkened the skies as far away as New England.

The American public was shocked by the death and destruction wrought by the Great Fire, and politicians demanded to know how such a massive blaze was allowed to rage uncontained. Defenders of the fledgling Forest Service said that the tragedy could have been avoided if the agency had more funding and more manpower. Congress responded by doubling the Forest Service’s budget.

In the aftermath of the Great Fire, Forest Service leadership adopted a strict policy of “total fire suppression.” The only way to prevent a catastrophic wildfire was to extinguish small fires quickly and completely. That meant more firefighters, more equipment and better training.

There were calls for more research into traditional methods of controlled burns or “light burning,” but the Forest Service dismissed the practices as dangerous.

Henry Graves, who led the agency during this period, wrote in 1912, “The doctrine of light burning as popularly understood in California is nothing less than the advocacy of forest destruction, and those who preach the doctrine have a large share of responsibility for fires which their influence has caused.”

In the wake of the Great Fire, fire in all of its forms was cast as the enemy of man. The firefighters who lost their lives in 1910 were hailed as fallen heroes. To defeat wildfires for good, America was prepared to wage a full-scale war on fire.

Over the next decades, the Forest Service was directed by three chiefs who had personally fought the Great Fire. They brought a military mentality and efficiency to the task of wildfire suppression, building access roads, erecting watchtowers and deploying thousands of men serving in the Depression-era Civilian Conservation Corps.

In 1935, in response to several bad wildfire seasons, the Forest Service adopted its “10 a.m. policy.” Firefighters were commanded to do everything possible to extinguish an active fire by 10 a.m. the next day. The urgency of the 10 a.m. policy drove the adoption of early detection methods like airplane surveillance and quick-response tactics like parachuting “smokejumpers,” who went into service in 1941.

After World War II, firefighting methods were aided by military technologies like chemical fire suppressants dropped from bomber jets and satellite surveillance.

“The increased sophistication of the technology alongside the militarized command structure—that was a Cold War approach being applied to wildfires,” says Deverell.

As early as 1920, the Forest Service established a public relations office to educate the public on the fact that nearly half of all wildfires on public lands were started by people. After experimenting with different messaging campaigns, the PR team settled on a motto: “Only you can prevent forest fires.”

Smokey Bear became the furry face of fire prevention in 1944 when he first appeared on safety posters pouring a bucket of water on a campfire. By the mid-1950s, Smokey was a bonafide celebrity and every child in America was indoctrinated into the dangers of an unwatched fire. For a time, Smokey Bear received more mail than the White House.

It wasn’t until the 1970s that the Forest Service was ready to reconsider the effectiveness of its decades-long war on wildfire. The zero-tolerance policy was successful in containing 98 percent of wildfires, but millions of acres continued to burn from just a few truly catastrophic blazes.

As Indigenous people had long known, new research confirmed that fire played a positive role in many Western forests. Periodic wildfires, if left to burn in non-populated areas, reduced the overall fuel load and slowed the spread of future fires. In recent decades, the Forest Service has continued to adapt its “let-burn” policies to contend with climate change and “exurban sprawl”—the encroachment of homes into wild spaces.

For his part, Smokey Bear has also changed his thinking on the inherent danger of fire.

“In 2001, Smokey Bear's motto changed,” says Deverell. “It went from ‘Only you can prevent forest fires” to ‘Only you can prevent wildfires.’ That reflects a tacit understanding on the part of the Forest Service that not all fire is ‘bad fire.’”