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The Standing Rock protests: A look at how we got here

Sean Rossman
Army veteran James White, a member of the Lakota Native American tribe, makes a snow angel on a closed bridge during a protest across from police protecting the Dakota Access oil pipeline site in Cannon Ball, N.D., Dec. 1, 2016.

Corrections and clarifications: an earlier version of this story didn't make clear the location of Lake Oahe.

There's been a lot of discussion about the pipeline protest at Standing Rock in North Dakota. So what exactly is going on and why is it important?

For one, it's the longest-running protest in modern history. It's been going on for months with protestors camping out in sometimes freezing temperatures and engaging in violent clashes with law enforcement, who have used tear gas and water cannons to quell the demonstrations.

Here's what you need to know:

What is the pipeline?

The $3.8 billion pipeline is mostly complete except for a portion underneath Lake Oahe and bordering Standing Rock Sioux Reservation in south North Dakota.

The nearly 1,200-mile pipeline, which is owned by Texas-based Energy Transfer Partners LP, will carry domestic crude oil from North Dakota production areas to Illinois. The company says the pipeline, which will carry about 470,000 barrels of oil a day, will move the oil in a more cost-effective and environmentally responsible manner.

Why are people mad?

Environmental activists and Native Americans say should the pipeline spring a leak, it could contaminate the area's water. Also, construction on the pipeline may threaten sites held sacred by Native Americans, including some said to contain burial grounds and cultural artifacts.

Standing Rock: What makes a person join the pipeline protest?

The protest started with just a few people in nearby Cannonball, North Dakota months ago. Now estimates put the encampment between 1,000 and 3,000 people. This weekend, about 2,000 veterans will arrive to take over for protestors who have endured weeks of confrontation with authorities.

Protesters demonstrate in solidarity with members of the Standing Rock Sioux tribe in North Dakota over the construction of the Dakota Access oil pipeline in Philadelphia, Dec 1, 2016.

Have the protests erupted into violence?

Yes. Law enforcement agencies have met protestors with pepper spray, tear gas, dogs, rubber bullets and even water cannons in below-freezing temperatures.

A 21-year-old woman said her left arm faces amputation after she was hit by a "concussion grenade."

Officers reported protestors fought back by throwing rocks, burning logs and launching stones using slingshots.

4 ways the Dakota Access Pipeline could be stopped

How the Dakota Access pipeline battle unfolded