Activists around the globe celebrated after the Army Corps of Engineers announced it will suspend work on the controversial Dakota Access Pipeline and consider rerouting the project.
Donald Trump's dramatic unblocking of the Dakota Access Pipeline project has set the stage for a new confrontation with native Americans and environmentalists.
Members of the Standing Rock Sioux Tribe and their supporters have protested against the pipeline at a North Dakota site for months, arguing the multi-billion dollar project would contaminate drinking water and damage sacred burial sites.
He signed permits for both Dakota and the Keystone XL pipelines within days of taking office as US president.
Though the decision marked a major victory for Native Americans and protesters, the fight may not be over just yet.
What is Dakota Access?
The temporary halt comes more than a month before President-elect Donald Trump, who supports the pipeline, takes office, which means he could reverse the decision.
A $3.7bn (£2.8bn) pipeline is planned at nearly 1,200 miles (1,900km) long to transport some 470,000 barrels of crude oil a day across four states, from North Dakota to a terminal in Illinois, where it can be shipped to refineries.
As the fate of the project hangs in the balance, here is a look at back at the controversy behind it.
The pipeline would provide a more cost-effective, efficient means of transporting crude, rather than shipping barrels by train.
What is the Dakota Access pipeline?
The project, built by a subsidiary of Texas-based company Energy Transport Partners (ETP), would also increase profit margins for oil companies while crude prices are low.
The $3.7bn (£2.8bn) pipeline is planned at nearly 1,200 miles (1,900km) long and will transport some 470,000 barrels of crude oil a day across four states, from North Dakota to a terminal in Illinois, where it can be shipped to refineries.
Most of the pipeline has already been built but the section closest to the Standing Rock Sioux reservation was still awaiting federal approval.
The pipeline will provide a more cost-effective, efficient means of transporting crude, rather than shipping barrels by train.
Why was it suspended?
The project, built by a subsidiary of Texas-based company Energy Transport Partners, will also increase profit margins for oil companies while crude prices are low.
The US Army Corps of Engineers, which has approval authority, suspended the project last year saying further analysis was needed.
What is the controversy about?
The decision came after months of protests by the Standing Rock Sioux Tribe and their supporters, who set up a Sacred Stone spiritual camp near the Missouri river.
The Sioux Native American people of Standing Rock argue the pipeline has unearthed and will go on to disturb various ancestral sites, including stone circles and sacred ground, if it is built.
They had argued that project would contaminate drinking water and damage sacred burial sites.
The sites are technically just north of the tribe's reservation but the Sioux say the government took this land from them illegally in a series of treaties in the 1850s and 1860s.
Construction sites are technically just north of the tribe's reservation but the Sioux say the government took this land from them illegally in a series of treaties in the 1850s and 1860s.
The tribe also say the pipeline could leak and contaminate their drinking water.
Native Americans also accused the government of approving pipeline construction without consulting them, a requirement under US law.
It is projected to run under the Missouri river, just north of their reservation. The Sioux started protesting in April, setting up Sacred Stone spiritual camp near the river.
Environmental activists say the pipeline would perpetuate fossil fuel production.
Native Americans have also accused the government of approving pipeline construction without consulting them, a requirement under US law.
What does Trump's decision mean?
Environmental activists have joined in protests with the tribe, saying the pipeline will perpetuate fossil fuel production.
Signing the permit, the US president said he approved Dakota Access and Keystone XL on condition that American steel be used.
Although the vast majority of Dakota Access oil pipeline has been built, the section closest to the Standing Rock Sioux reservation is still awaiting federal permits and approval.
Dakota, he said, would be "subject to terms and conditions negotiated by us".
Who are the protesters?
The new president may face questions about his personal interest in the Dakota project as ETP chief executive Kelcy Warren donated $100,000 (£80,000) to his election campaign.
The demonstrators include environmental activists, citizens supporting the cause, the Sioux and other native tribes who have joined to show solidarity with the Sioux.
Mr Trump denies he is motivated by any financial interest.
More than 200 Native American tribes have pledged their support to the movement. It is the largest coming together of indigenous peoples in the US in decades, perhaps centuries.
How have opponents of the project reacted?
In a statement quoted by Reuters news agency, the Standing Rock Sioux said they would fight the decision.
"Americans know this pipeline was unfairly rerouted towards our nation and without our consent," they said.
Greenpeace director Annie Leonard said that "instead of pushing bogus claims about the potential of pipelines to create jobs, Trump should focus his efforts on the clean energy sector where America's future lives".
Who exactly are the protesters?
More than 200 Native American tribes pledged their support last year, in the largest coming together of indigenous peoples in the US in decades, perhaps centuries.
Oceti Sakowin Camp has been home to an estimated 4,000 people who travelled to the site to join in the demonstrations.
Oceti Sakowin Camp has been home to an estimated 4,000 people who travelled to the site to join in the demonstrations.
Several actors including Shailene Woodley and Mark Ruffalo, Green Party presidential candidate Jill Stein as well as Democratic presidential primary contender Bernie Sanders have also rallied alongside protesters.
Among others lending their support were
Hundreds of US military veterans joined the activists last week. The campaigners have endured bitter temperatures and had been ordered to leave the area by Monday.
Have the demonstrations been peaceful?
Have the demonstrations been peaceful?
While the Native Americans have said they are committed to peaceful unarmed protests, demonstrations have turned violent.
Protesters have been accused of starting fires and throwing petrol bombs at police.
Police deployed at the protests have also been accused of beating peaceful demonstrators while local law enforcement have characterised them as rioters and the protests as unlawful.
A Colorado woman who shot at police trying to remove protesters from private property was arrested and charged with attempted murder.
Last month, a Colorado woman fired three shots in the direction of police as officers sought to forcibly remove protesters camped on private property. The woman was arrested and has been charged with attempted murder.
Police have in turn been accused of using excessive force, including dousing crowds with pepper spray and freezing water as well as firing sound cannons, bean bag rounds and rubber bullets.
Other reports say protesters have started fires and thrown debris at officers, including petrol bombs.
Protesters are divided in their response to the authorities. Some militant activists have called for aggressive tactics while others insist demonstrations must not break the law.
On 25 November the US Army Corps of Engineers issued a letter calling for the Oceti Sakowin camp, which sits on federally owned land, to be evacuated by 5 December.
This was followed by a similar evacuation order from the governor of North Dakota, citing harsh weather conditions.
How have authorities responded?
Police have been criticised for using excessive force, including dousing crowds with pepper spray and freezing water as well as firing sound cannons, bean bag rounds and rubber bullets.
Jacqueline Keeler from the Sioux tribe told the BBC: "They used a sonic device and then also they used rubber bullets and we have shots of people who had rubber bullets right to the face.
"They Mace'd elders right in the face. They dragged people out of sweat lodges [steam baths]. They shot one 15-year-old boy's horse and killed it under him."
Officers have arrested hundreds of people and accused activists and journalists of criminal trespass, rioting and other felonies.
Officers have arrested hundreds of people and accused activists and journalists of criminal trespass, rioting and other felonies.
The United Nations Human Rights office has criticised local law enforcement and Dakota Access LLC security staff for committing abuses against indigenous protesters, issuing a statement on 15 November.
At one point, police held protesters in temporary cages made of chain-link, which activists equated to "dog kennels".
During mass arrests last month, police held protesters in temporary cages made of chain-link, which activists equated to "dog kennels".
Whom would the pipeline benefit?
The local Morten County police are being sued for excess force by a number of camp residents.
They deny any violations, and have repeatedly accused the self proclaimed "water protectors" of acting illegally.
Who would the pipeline benefit?
The pipeline would benefit oil companies, shareholders and local governments. Dakota Access says the project will create between 8,000-12,000 jobs and generate $55m in annual property taxes.
The pipeline would benefit oil companies, shareholders and local governments. Dakota Access says the project will create between 8,000-12,000 jobs and generate $55m in annual property taxes.
The project could also be advantageous to President-elect Donald Trump, who has had stocks in Texas-based Energy Transfer Partners, the Dakota Access builder, and Phillips 66, which owns one-quarter of the pipeline.
Mr Trump, who supports the project, denies his policy is based on any financial interest.
Campaign finance records also show that Kelcy Warren, the CEO of Energy Transfer Partners, donated more than $100,000 (£80,437) to Mr Trump's presidential campaign.
Farmers could also benefit. North Dakota's crude oil is currently shipped out by train which has caused congestion and rail delays, slowing the shipment of grain and increasing grain prices.
Farmers could also benefit. North Dakota's crude oil is currently shipped out by train which has caused congestion and rail delays, slowing the shipment of grain and increasing grain prices.
What are the legal issues?
The Sioux had filed a suit against the Army Corps of Engineers, the agency that typically approves inter-state pipelines, for permitting Dakota Access construction without proper consultation.
According to US law, federal agencies are required "to consult with Indian tribes when they attach religious and cultural significance to a historic property regardless of the location of that property".
Native American tribes by law govern themselves. Tribes also enjoy a "government-to-government" relationship with federal authorities, protected by the US Constitution. The Sioux say these provisions were ignored in the pipeline construction.
In September the federal government temporarily blocked pipeline construction under the Missouri, close to the Standing Rock Reservation. Although this ruling is binding until further notice, construction elsewhere along the pipeline's route is not prohibited and has continued.
What happens now?
The Army Corps of Engineers has said it will not grant a permit to allow the pipeline to cross under the lake until it explores alternate routes.
The corps' said the best way to reroute the project would be through a lengthy environmental review, which could take months or years.
The future of the pipeline, however, hinges on whether the Trump administration will allow the corps to proceed with the review or allow the completion of the original route.
As for protesters, Standing Rock Sioux Chairman Dave Archambault asked non-Sioux protesters to return home after Sunday's announcement.
"I'm asking them to go. Their presence will only cause the environment to be unsafe," he said.
But some activists are planning to stick around.
"We know that these prayers are powerful…we have to be ready, though," said activist Tom Goldtooth, of the Indigenous Environmental Network.
"We're going to accept this as a victory. But this is one battle in the broader war."
