It was near the end of September, an unusually warm week in 1871, and William “Buffalo Bill” Cody and a group of wealthy New Yorkers stood atop a grassy hill near the Platte River in Nebraska, where two miles off they spotted six huge brown beasts.

Cody was a legend of the frontier era, part myth conjured in dime novels. The men from New York had expected to find him as a “desperado of the West, bristling with knives and pistols,” but they did not. Cody was loquacious and friendly, an expert hunter. He knew that with the wind blowing from behind, the men risked their scent being carried to the animals and scaring them away. Then again, a buffalo is a lumbering, hirsute cow, and the men were outfitted with some of the quickest horses and held the best guns owned by the U.S. Army, which was outfitting the hunting expedition. The Army wasn’t in the business of guiding hunting trips for soft-skinned Wall Streeters, but it was in the business of controlling the Native Americans in the area, and that meant killing buffalo. One colonel, four years earlier, had told a wealthy hunter who felt a shiver of guilt after he shot 30 bulls in one trip: "Kill every buffalo you can! Every buffalo dead is an Indian gone.”

Cody and the men made a contest of the hunt. Whoever killed the first buffalo would win an engraved silver chalice. Years later, in an article he wrote for the magazine Cosmopolitan, Cody would call this trip the best equipped he’d ever taken. The Army had supplied an armed escort and 25 wagons filled with cooks, linen, china, carpets for their tents, and a traveling icehouse to keep their wine chilled. The reason for such extravagance was undoubtedly because the New Yorkers were well-connected, but also because Major-General Phillip Sheridan, the man with the task of forcing Native Americans off the Great Plains and onto reservations, had come along with them. This was a leisure hunt, but Sheridan also viewed the extermination of buffalo and his victory over the Native Americans as a single, inextricable mission––and in that sense, it could be argued that any buffalo hunt was Army business. After the men circled the herd, they charged down the hill, chasing after the six buffalo, eager for the first kill.

On Monday, President Obama signed the National Bison Legacy Act, making the American bison––or the buffalo as it’s more often called––the national mammal. It’s only the second animal to represent the U.S., joining the bald eagle. It’s ironic, of course, because at one time American settlers and hide-hunters killed the animal to near-extinction, and tourists shot the animals from the windows of trains as if the slaughter could last forever. Buffalo had once numbered more than 30 million, and by the end of the 19th century there were only a few hundred in the wild. Today, some 20,000-25,000 remain in public herds.

Many things contributed to the buffalos demise. One factor was that for a long time, the country’s highest generals, politicians, even then President Ulysses S. Grant saw the destruction of buffalo as solution to the country’s “Indian Problem.”

Before Sheridan joined Cody and the New Yorkers on the hunt, and before he oversaw the relocation of Native Americans on the plains, he was a major-general for the Union during the Civil War. It was there he learned the power of destroying enemy resources. He’d used the same scorched-earth strategy that William Tecumseh Sherman, then a major-general, used in his March to the Sea, tearing  up railroad ties, toppling telegraph poles, and lighting nearly all of Atlanta and anything an infantryman could digest ablaze. After the war, President Grant asked Sherman and Sheridan to command armies in the Great Plains.

This was Manifest Destiny, and there’d never be enough room for Native Americans and white settlers. In treaty after reneged treaty, the land granted to the tribes of the Great Plains shrunk. The U.S. wanted them docile, to take up farming on the reservations and stay put. But the Sioux, the Kiowa, and Comanches, nearly all the tribes of the plains, lived alongside buffalo herds and took from them their skins for tents, and their meat for food.

When miners discovered gold in Montana, in some of the best hunting grounds in the country, the Sioux fought the white settlers rushing to extract yet another profitable resource from their land. That escalated into a small war, and eventually what’s called the Fetterman Fight, named after the U.S. Army captain leading the troops. The Sioux killed Captain William J. Fetterman and all 80 of his men. At that time, it was the worst loss the U.S. had ever suffered on the Great Plains. In 1868, Sherman and a peace commission signed the Fort Laramie Treaty with the Sioux and outlined for them a reservation. Part of the treaty also allowed the Sioux to hunt buffalo north of the Platte River––almost the same land where Cody and the New Yorkers would hunt three years later. Sherman hated the idea. He was “utterly opposed to that clause of the treaty,” wrote David D. Smits in The Western Historical Quarterly. “He was determined to clear the central plains region between the Platte and the Arkansas of Indians so that the railroads, stage lines, and telegraph could operate unmolested.”

Sherman knew that as long as the Sioux hunted buffalo, they’d never surrender to life with a plow. In a letter to Sheridan, dated May 10, 1868, Sherman wrote that as long as buffalo roamed those parts of Nebraska, “Indians will go there. I think it would be wise to invite all the sportsmen of England and America there this fall for a Grand Buffalo hunt, and make one grand sweep of them all.”

By now the buffalo that once covered all the Great Plains were hewn into two giant herds––one in the north, and one in the south. Still, the brown herds could overwhelm, and when Sheridan asked a trader how many buffalo he thought lived in the southern herd, the man said 10 billion. Obviously, that was absurd. But if the Army planned to slaughter all buffalo and starve the tribes into submission, it’d take more time and men than Sheridan had. Still, there’s evidence he thought it the best option: In October 1868, Sheridan wrote to Sherman that their best hope to control the Native Americans, was to “make them poor by the destruction of their stock, and then settle them on the lands allotted to them.”

Soon Sherman would have help. But along with the Fort Laramie Treaty, the U.S. had also signed the Medicine Lodge Treaty in 1867 with tribes in the south. So for the moment, The Indians Wars had paused.

In the lull, enlisted men like Cody found other ways to stay busy, and to make money. Cody had joined the Cavalry at 17, and he earned the name “Buffalo Bill” because in one 18-month stretch he claimed to have killed 4,280 buffalo. In 1870, a bull hide sold for $3.50. One frontiersman, Frank Mayer, figured if he spent 25 cents on each round of ammo, then “every time I fired one I got my investment back twelve times over.”

Buffalo were slow-grazing, four-legged bank rolls. And for a while, there were plenty. Then in 1873 an economic depression hit the country, and what easier way was there to make money than to chase down these ungainly beasts? Thousands of buffalo runners came, sometimes averaging 50 kills a day. They sliced their humps, skinned off the hides, tore out their tongues, and left the rest on the prairies to rot. They slaughtered so many buffalo that it flooded the market and the price dropped, which meant they had to kill more. In towns, hides rose in stacks as tall as houses. This was not the work of the Army. It was private industry. But that doesn’t mean Army officers and generals couldn’t lean back and look at it with satisfaction.

“I read that army commanders were even providing bullets to these hunters,” said Andrew C. Isenberg, author of The Destruction of the Bison, and a professor of history at Temple University. “The military looked at what the private sector was doing and they didn’t need to do anything more than stand back and watch it happen.”

Isenberg said though it was never official policy to kill buffalo in order to control Native Americans on the plains, the Army was certainly conscious about it. And at least in action, Isenberg said, “they were extremely explicit about it.”

Herds became harder to find. In some prairies, they’d completely vanished. The buffalo runners sent two men to Fort Dodge, Kansas, to ask the colonel there what the penalty was if the skinners crossed into the Texas Panhandle and onto reservation land. The Medicine Lodge Treaty said no white settlers could hunt there, but that’s where the remaining buffalo had gathered. Lieutenant Colonel Richard Dodge met with the two men, and one remembered the colonel say, “Boys, if I were a buffalo hunter I would hunt buffalo where buffalo are.” Then the colonel wished them good luck.

In the next decade, the hide hunters exterminated nearly every buffalo. Colonel Dodge would later write that “where there were myriads of buffalo the year before, there were now myriads of carcasses. The air was foul with a sickening stench, and the vast plain which only a short twelve months before teemed with animal life, was a dead, solitary desert.”

The wasteland was so scattered with the bones of dead animals and buffalos that all the prairie felt like a graveyard risen. One judge called it a “charnel house, with so many skulls staring at a man, and so many bones that newcomers felt nervous.”

During a hard drought, with no buffalo left, settlers and Native Americans hunted their bones, selling them for fertilizer. In Isenberg’s book, he tells about a reporter who asks a railroad worker, “‘Do the Indians make a living gathering these bones?’ Yes, replied a railroad inspector, “but it is a mercy that they can’t eat bones. We were never able to control the savages until their supply of meat was cut off.’”

Some men saw the future. And even before the buffalo runners had wiped out almost every animal and the U.S. Army had to protect the last remaining wild herd in Yellowstone National Park, conservationists lobbied Congress to pass a bill that’d save buffalo. It did not sit well with Sheridan. No record exists of his words, but one hide hunter later said Sheridan had defended the industry to legislatures by saying: “These men have done in the last two years, and will do more in the next year, to settle the vexed Indian question, than the entire regular army has done in the last thirty years.”

Congress passed the bill to protect buffalo in 1875, but President Grant refused to sign it. The peace treaties had failed, and in that same year, in what’s called the Red River War, the U.S. beat back the Comanche, the Kiowa, Cheyenne, and the Arapaho on the southern plains and forced them into reservations. Without buffalo, the U.S. government delivered cattle to some tribes. When the Oglala Lakota in the north mounted horses and killed the cows in ritual as they had the buffalo on their prairie hunts, the government stopped sending live cows and instead shipped meat from a nearby slaughterhouse. The Oglala Lakota burned the slaughterhouse down.

But that was all some time away. It’d be another four years before the buffalo-protection bill died, and the Native Americans resigned to reservations, from when Cody and the U.S. Army and the men from New York stood on the grassy hill, in that unusually warm September in 1871, above the Platte River in Nebraska.

Cody and the men had circled their horses around the herd until they were downwind. A buffalo can weigh 2,000 pounds, run 35 mph, and quickly pivot to fight with horns that can rip flesh like obsidian. When the men were close enough, Cody gave the signal to charge. He and the men from New York thundered toward the six buffalo, hoping to win the silver trophy, excited to kill. Of the moment, one man wrote:

“The buffalo, as usual, took one good look at their enemies, and then, wheeling around and stretching their tails straight in the air, set off, full gallop, in Indian file, at a pace that tested the best powers of the horses to surpass. Just as they started, our main body emerged from its concealment, and had a full view of the whole hunt, a most exciting and interesting sight to those new to the plains. On came the six huge buffalo, one behind the other, all running together as regularly as if kept in their places by some rule of drill, and close behind them the hunters, each horse doing his best, and now one leading and then another, as though in a hotly contested race.”