So, a long time ago in a place called Prussia, there were lots of different churches with different ideas about how to worship God. Some people followed the Lutheran church and some followed the Reformed church. They were all a bit confused and didn't know how to get along.
Then, one day, the king of Prussia decided to make things easier by creating something called the Prussian Union of Churches. This meant that all the different churches would come together and become one big church. They would still have their own ideas about how to worship God, but they would all respect each other.
The king hoped that this would stop people from arguing and fighting about religion, and it did make things simpler for the government too. But not everyone was happy with this idea. Some people still wanted to follow their own church, and felt like they were being forced to do something they didn't believe in.
So, the Prussian Union of Churches helped to bring people together, but it also created some problems too. And that's how the church joined forces in Prussia!