BISMARCK, N.D. (AP) — Law enforcement in North Dakota moved in Thursday to remove activists protesting the Dakota Access oil pipeline who had set up a camp on private property owned by the pipeline developer. Here's a guide to the latest developments and key background about the protest:

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THE ORIGINS

Dallas-based Energy Transfer Partners got federal permits for the $3.8 billion pipeline in July, about two years after it was announced. The project is projected to move a half-million barrels of crude oil daily from western North Dakota through South Dakota and Iowa to an existing pipeline in Patoka, Illinois, for shipment to Midwest and Gulf Coast markets.

Supporters say the pipeline will have safeguards against leaks, and is a safer way to move oil than trucks and trains, especially after a handful of fiery — and sometimes deadly — derailments of trains carrying North Dakota crude.

But the Standing Rock Sioux, other tribes and environmental groups say that the pipeline could threaten water supplies for millions, since it will cross the Missouri River, as well as harm sacred sites and artifacts. Protesters, sometimes numbering in the thousands, have gathered since April at the confluence of the Cannonball and Missouri rivers in southern North Dakota.

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IN THE COURTROOM

The Standing Rock Sioux, whose reservation straddles the North Dakota-South Dakota border, are suing federal regulators for approving the oil pipeline. They have challenged the U.S. Army Corps of Engineers' decision to grant permits at more than 200 water crossings and argue that the pipeline would be placed less than a mile upstream of the reservation, potentially affecting drinking water for more than 8,000 tribal members and millions downstream.

The tribe hasn't fared well in court so far. A federal judge in September denied their request to block construction of the entire pipeline. Three federal agencies stepped in and ordered a temporary halt to construction on corps land around and underneath Lake Oahe — one of six reservoirs on the Missouri River.

The corps is reviewing its permitting of the project and has given no timetable for a decision. Meanwhile, the tribe's appeal is still pending in federal court.

Energy Transfer Partners has said construction is nearly complete elsewhere.

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THE PROTESTS

The tribe's fight grew into an international cause in recent months for many Native Americans and indigenous people from around the world, with some traveling thousands of miles to join the protest.

"Divergent" actress Shailene Woodley also protested and was arrested. "Democracy Now!" host Amy Goodman was charged with rioting and trespassing stemming from her coverage of a protest, but the charges were later dropped.

More than 260 people have been arrested since the larger demonstrations began in August.

As of Wednesday, nearly all of the $6 million in emergency funding earmarked for law enforcement costs related to the protest had been used up. The state's Emergency Commission approved the money in late September, and the Department of Emergency Services plans to ask for more.

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LATEST DEVELOPMENTS

The protests entered a new phase over the weekend when some 200 protesters moved onto private land along the pipeline route that had recently been acquired by Energy Transfer Partners.

Law enforcement asked protesters to leave peacefully on Wednesday and were refused. On Thursday, some 200 officers in riot gear moved in to remove the protesters, wielding pepper spray and firing bean-bag rounds from shotguns.

Donnell Hushka, a spokeswoman for the Morton County Sheriff's Department, said 141 people were arrested.

Morton County Sheriff Kyle Kirchmeier said officers would stay on the site to make sure protesters don't re-occupy it or block highways in the area.