Okay kiddo, so there are lots of churches in America -- places where people go to worship together and learn about their religion. But sometimes, people don't agree on everything about their religion, so they start their own church with their own rules.
That's what happened with the American Church Union. A long time ago, some people who were part of the Episcopal Church (which is a type of Christian church), didn't like some of the changes that were being made in their church. They wanted to keep things the way they used to be, with older traditions and rituals.
So, they started their own church, called the American Church Union. They wanted to keep the traditional teachings and beliefs of the Episcopal Church, but without any of the changes they didn't like.
The American Church Union is still around today, but it's not as big as some other churches in America. Some people continue to go to this church because they prefer the older traditions and rituals, while other people prefer going to different churches that have different traditions and ways of worshiping.
I hope that helps, buddy! Do you have any more questions?