Okay, imagine you're at school and you and your classmates need to decide on some new rules for the school. Your teacher would probably let everyone have a say and then take all the ideas and put them together to make some new rules that everyone can agree on, right? That's kind of like what happened with something called the Plenary Councils of Baltimore.
Back a long time ago, in the 19th century, the Catholic Church in the United States was growing very fast. That's because a lot of people were coming over from Europe and they were already Catholic. But as the Church grew, they had some new problems to deal with. They needed to figure out how to help all the new people who were becoming Catholic, what to do about some new ideas that were starting to pop up, and how to work together better as a Church.
So, in 1852, the bishops (the leaders of the Church) decided to have a big meeting in Baltimore, Maryland, to figure all of this out. They called it a Plenary Council, which just means everyone from the Church coming together to talk about important things. At this meeting, they came up with some new rules and ideas to help the Church grow and be better.
But that was just the first Plenary Council. Over the next seventy years, there were three more! Each time, the bishops would come together, talk about what was happening and how they could help the Church, and then come up with some new rules and guidelines. Some of these things were about how to do Mass, how to prepare people for becoming Catholic, and what to do about people who disagreed with the Church.
Overall, the Plenary Councils of Baltimore helped the Catholic Church in the United States grow and become stronger. It's kind of like when you and your classmates get together and decide on some new rules for the school. You all work together to make things better and that's what the Plenary Councils of Baltimore did for the Catholic Church.