It fought to save the whales. Can Greenpeace save itself?

Now, Greenpeace's very existence is under threat: A lawsuit seeks at least $300 million in damages. Greenpeace has said such a loss in court could force it to shut down its American offices. In the coming days, a jury is expected to render its verdict.

The lawsuit is over Greenpeace's role in protests a decade ago against a pipeline near the Standing Rock Sioux Reservation in North Dakota. The pipeline's owner, Energy Transfer, says Greenpeace enabled illegal attacks on the project and led a "vast, malicious publicity campaign" that cost the company money.

Greenpeace says that it played only a minor, peaceful role in the Indigenous-led protest, and that the lawsuit's real aim is to limit free speech not just at the organization, but also across America, by raising the specter of expensive court fights.

The suit comes at a time of immense challenges for the entire environmental movement. Climate change is making storms, floods, and wildfires more frequent and more dangerous. The Trump administration has commenced a historic effort to overturn decades of environmental protections. Many of the movement’s most significant achievements over the past half-century are at risk.

Sushma Raman, interim executive director of Greenpeace USA, has called the trial in North Dakota "a critical test of the future of the First Amendment."

Energy Transfer, one of the biggest pipeline companies in the country, has said that the lawsuit is over illegal conduct, not free speech. "It is about them not following the law," the company said in a statement.

Founded in Vancouver in 1971, Greenpeace was hugely successful early on at what is now called “branding,” with its catchy name and daredevil stunts. But it has also faced major challenges: infighting, missteps, legal battles, and questions about how to widen its base and remain relevant as it became an institution.

Greenpeace was founded as an offshoot of the Sierra Club based on the principles of ecology and antimilitarism. But pulling off daring stunts in pursuit of those principles, while also operating as a worldwide professional network, has always been a delicate balancing act.

After friction and fights for control of the organization in the late 1970s, Greenpeace International was established in the Netherlands as the head office, coordinating the activities of independent Greenpeace offices around the world, including Greenpeace USA.

The activities of its US branch are at the center of the lawsuit. Greenpeace International says its role was limited to signing one open letter. Greenpeace International has also countersued Energy Transfer in the Netherlands, seeking to recoup its legal costs under European laws that essentially allow it to challenge the Energy Transfer lawsuit as a form of harassment.

Greenpeace was born out of a moment of fear and upheaval, amid the Vietnam War, the nuclear arms race, acid rain and smog blanketing cities. Rex Weyler, 77, an early member, chronicled the history in his 2004 book "Greenpeace: How a Group of Ecologists, Journalists and Visionaries Changed the World."

In Vancouver, Weyler met Bob Hunter, a columnist for the Vancouver Sun, and Dorothy and Irving Stowe, older Quakers who had left the United States in protest over war taxes and weapons testing.

They would soon become an offshoot of a more traditional environmental group, the Sierra Club, after a disagreement over protest tactics.

Their first campaign was a mission to block US nuclear weapons tests on Amchitka, a volcanic island in Alaska. An idea this group had floated within the Sierra Club — to sail a boat to stop the bomb — had been reported in the Vancouver Sun, though the head office of Sierra Club in San Francisco had not approved that plan.

"The Sierra Club was not amused when they saw this story, because they said, 'You know, a lot of our members are just tree-huggers, and they don't care about nuclear disarmament,'" said Robert Stowe, son of Dorothy and Irving and a behavior neurologist. "Had the Sierra Club agreed to do this, Greenpeace could probably never have been founded."

The boat set sail in September 1971. The Coast Guard intercepted it, and the vessel never reached Amchitka. But the stunt garnered considerable public attention, a core part of the group's strategy in the years since.

Greenpeace's next campaign is perhaps its most well known: saving the whales.

The idea came from Paul Spong, who had studied orca whales and argued that the highly intelligent creatures were being hunted to extinction. That led to a copiously documented, dramatic sailing expedition to confront Soviet whaling ships.

A worldwide moratorium on commercial whaling has been in place since 1986. Greenpeace and other groups who worked on the issue have claimed it as a major victory.

The group also tried to stop seal hunting in northern Canada, a controversial move that alienated a large number of residents, including in Indigenous communities. Greenpeace Canada apologized to the Inuit people for the impacts of the campaign in 2014.

In 2014, when there was an uproar in Peru over a Greenpeace action that damaged the Nazca lines, ancient man-made patterns etched in the desert. Activists from Greenpeace Germany entered the restricted area to place a protest message about renewable energy.

The organization apologized, and the episode prompted Greenpeace USA to adopt a formal policy to not get involved in struggles led by Indigenous people unless specifically asked to do so.

That policy has come up in this month's trial in North Dakota. Greenpeace argued that it had offered support in the Dakota Access Pipeline protest only after it was asked to do so by Indigenous leaders and did not seek any major role in the demonstrations.

On Monday in a courtroom in the small city of Mandan, N.D., jury members are expected to start hearing closing arguments, after which they will consider Greenpeace’s fate.

This article originally appeared in The New York Times.