This story was originally published by Mother Jones and is reproduced here as part of the Climate Desk collaboration.

Ome Tlaloc walked through the North Dakota hills with a flashlight and a walkie-talkie, scouting for police in the prairie dark. Earlier that evening, I’d met the 30-year-old on Highway 1806, where he’d been sitting behind a makeshift barricade. Now he was doing reconnaissance. The Morton County Sheriff’s Department and the National Guard, stationed ahead of us on the road, were planning to raid the camp where Tlaloc and hundreds of other protesters had been living for the past week. The barricade was meant to stop the cops, or at least to slow them down. As he walked, Tlaloc listened to his radio for the code words that would signal when he and his comrades were to spring into action: “Eagle’s Claw.”

The Standing Rock Sioux reservation sits in the Dakota Prairie Grasslands, an endless sweep of elephan­tine hills once home to millions of members of the Lakota Nation. Today, it’s inhabited by fewer than 9,000 of their surviving descendants, and one of the few places in America where buffalo roam wild. In late July, the Dallas-based Energy Transfer Partners informed the Standing Rock Sioux that in five days its subsidiary would begin construction on a section of the Dakota Access Pipeline (DAPL) next to the reservation. After that, members of more than 200 Native American tribes and their allies gathered to block what would be America’s longest crude oil pipeline. Their encampments of teepees, tents, and RVs were mostly ignored by the media until private security guards set dogs on protesters and a few journalists were arrested, sparking a national conversation about tribal sovereignty, environmental racism, and police brutality.

The October night I met Tlaloc, the stakes in the #NoDAPL movement were as high as they’d ever been. If the “water protectors,” as the protesters called themselves, were cleared out, the pipeline would continue east under the Missouri River, coming within 1,500 feet of Lake Oahe, the Standing Rock Sioux’s water supply. A leak or spill, activists believed, would poison the drinking water of as many as 10 million people, nearly all of them on Native American reservations. The protesters’ goal was to block construction until March 2017, when Dakota Access would have to reapply for a federal construction permit — a delay that might make the project financially unfeasible. If the protesters were removed before then, Dakota Access would complete the 1,172-mile pipeline that would transport up to 570,000 barrels of crude a day. (On Dec. 4, the Army Corps of Engineers announced that it would not approve a permit for the pipeline to run beneath Lake Oahe.)

Dakota Access
Mother Jones / Zen Lefort

Tlaloc stopped at the top of a ridge. Off in the distance was the trench holding the lengths of 30-inch metal pipe. “An old Sioux prophecy says that a black snake will come to destroy the world at a moment of great uncertainty,” he said. “Unless the youth stop it.”

Back at the barricade, men in camo fatigues sipped cowboy coffee and waited. Pup tents formed a circle around a pit fire. “They’ve killed us before,” said Harry Beauchamp, a 63-year-old Assiniboine from Montana. Resting his cowboy boots on a soup pot, he told us about his participation in the 1973 standoff between members of the American Indian Movement and law enforcement agents in South Dakota that ended in the deaths of two Native American activists. A few weeks earlier, he’d been attacked by a dog brought in by a pipeline security contractor. His future son-in-law, he said, was bringing him a rifle. “I’m not going to let this be another Wounded Knee,” he said.

Dakota Access Native people tribe dancing
Mother Jones / Zen Lefort

The next day, a pale sun burned through the morning haze, backlighting 200 sheriff’s deputies and National Guardsmen in full riot gear. Behind them were an armored personnel carrier, a land-mine-resistant truck, and the pipeline’s private security force — overseen by TigerSwan, a North Carolina firm that’s done work for the U.S. government in Afghanistan and Iraq. “This is a state highway,” a police commander said into a loudspeaker. “You must clear the road.”

On Aug. 19, North Dakota Gov. Jack Dalrymple, who served as an adviser to Donald Trump’s presidential campaign, had declared a state of emergency, and the National Guard mobilized three weeks later. On Sept. 3, security contractors turned dogs on the protesters. Not long afterward, Standing Rock Sioux tribal Chair Dave Archambault II asked the Justice Department to investigate civil rights violations against activists. “This country has a long and sad history of using military force against indigenous people — including the Sioux Nation,” he wrote. “[W]hen I see the militarization taking place in North Dakota against Indian people, I am genuinely concerned.”