When 18 people walked onto the construction site of the Seabrook Nuclear Power Plant in New Hampshire on 1 August 1976, it was the first collective nonviolent direct action against nuclear power in the USA. Many opponents of nuclear power considered such tactics too radical. Later that month, when 180 people committed civil disobedience at the site, the organisers, the Clamshell Alliance, used nonviolence training and the affinity group structure for the first time. In the future, these elements became well-known and practised throughout the nonviolent social change movement. On 30 April 1977 over 2400 people, organised in hundreds of affinity groups, occupied the site. During the next two days 1415 were arrested, many jailed for two weeks. This action inspired the anti-nuclear power movement and created a new international model for organising actions that consisted of training for nonviolent direct action and consensus decision-making in a non-hierarchical affinity group structure.

Inspiration for the Seabrook action actually came from Europe. In the early 1970s, people in Germany and France became concerned about plans to build a nuclear power plant in Whyl, Germany. Nearby, across the border in Marckolsheim, France, a German company announced plans to build a lead factory alongside the Rhine. The people living in Whyl and Marckolsheim agreed to cooperate in a cross-border campaign, in August 1974 founding a joint organisation, the International Committee of 21 Environmental Groups from Baden (Germany) and Alsace (France). Together they decided that wherever the construction started first, together they would nonviolently occupy that site to stop the plants.

After workers began constructing a fence for the Marckolsheim lead plant, on 20 September 1974 local women climbed into the fencepost holes and stopped the construction. Environmental activists erected a tent, at first outside the fence line, but soon moved inside and occupied the site. Support for the campaign came from many places. The German anarcho-pacifist magazine Graswurzelrevolution had helped to spread the idea of grassroots nonviolent actions. A local group from Freiburg, Germany, near the plants, introduced active nonviolence to those organising in Whyl and Marckolsheim. In 1974, a three-day workshop in Marckolsheim included nonviolence training; 300 people practised role-plays and planned what to do if the police came.

People from both sides of the Rhine—farmers, housewives, fisherfolk, teachers, environmentalists, students and others—built a round, wooden 'Friendship House' on the site. The occupation in Marckolsheim continued through the winter, until 25 February 1975 when the French government withdrew the construction permit for the lead works.

Meanwhile, construction of the nuclear reactor in Whyl, Germany, had begun. The first occupation of that site began on 18 February 1975 but was stopped by the police a few days later. After a transnational rally of 30,000 people on 23 February, the second occupation of the Whyl construction site began. Encouraged by the success in Marckolsheim, the environmental activists, including whole families from the region, continued this occupation for eight months. More than 20 years of legal battles finally ended the plans for the construction of the Whyl nuclear power plant.

In the summer of 1975, two U.S. activists, Randy Kehler and Betsy Corner, visited Whyl after attending the WRI Triennial in the Netherlands. They brought the film 'Lovejoy's Nuclear War', the story of the first individual act of nonviolent civil disobedience against a nuclear power plant in the USA. They brought back to the USA and to those organising to stop the Seabrook nuclear power plant the inspiring story of the German community's occupations. More information exchange followed. During the 1976 occupation of Seabrook, WRI folks in Germany communicated daily by phone with the Clamshell Alliance. German nonviolent activists had been using consensus, but the affinity group structure was new to them, and they saw it as an excellent method for organising actions.

In 1977, German activists and trainers Eric Bachman and Günter Saathoff made a speaking trip to the USA, visiting anti-nuclear groups in the northeastern USA as well as groups in California where there were protests against a nuclear power plant at Diablo Canyon. Activists from both sides of the Atlantic continued this process of cross-fertilisation.

The Marckolsheim and Whyl plants were never built. Even though one of the two proposed nuclear reactors was built in Seabrook, no new nuclear power plants have started in the USA since then. Both Whyl in Germany and Seabrook in the USA were important milestones for the anti-nuclear movement and encouraged many other such campaigns.

The Clamshell Alliance at Seabrook, which was itself inspired by actions in Europe, in turn became a source of inspiration to others in the USA and in Europe. In the USA, the Seabrook action inspired the successful campaign to stop the Shoreham, Long Island, New York, nuclear power plant, then 80 percent completed. That began when an affinity group of War Resisters League members returned from the Seabrook occupation and began to organise in their community. British activists who took part in the 1977 occupation of Seabrook, together with activists who read about it in Peace News, decided to promote this form of organisation in Britain, leading to the Torness Alliance opposing the last 'green field' nuclear site in Britain. In Germany, a number of nuclear power plants and nuclear fuel reprocessing plants were prevented or closed due to growing protests. In the early 1980s, large nonviolent actions were organised in both Britain and Germany in opposition to the installation of U.S. cruise missiles, using the affinity group model. And the story has continued, with affinity groups being used in many nonviolent actions around the world (including in the 1999 sit-ins in Seattle to stop the World Trade Organisation meetings).