Okay, so let's talk about anti-nuclear groups in the United States. "Nuclear" means something that has to do with nuclear energy or nuclear weapons. Some people are very worried about nuclear things because they think they are very dangerous and could hurt lots of people.
These people have formed groups, which are like teams of people who work together for a common goal, to try to stop nuclear power plants from being built or to shut down existing ones. They also want to stop the government from using nuclear weapons.
One reason they are worried is because nuclear power plants use a lot of radioactive materials, which can be harmful to people if there is an accident or if something goes wrong. That's why they want to stop new power plants from being built or to shut down existing ones.
Another reason is that nuclear weapons are very powerful and can cause a lot of damage. They can kill lots of people and destroy entire cities. The people in these anti-nuclear groups think that using these weapons would be a very bad idea and could cause a lot of harm to innocent people.
So, in summary, some people are worried about nuclear energy and weapons because they think they are dangerous and could cause harm. They have formed groups to try to stop new power plants from being built or to shut down existing ones and to stop the government from using nuclear weapons.