Gleichschaltung is a very complicated word that was used in Germany during the time when a leader named Adolf Hitler was in charge.
Imagine you are in a playground where everyone is playing different games. Some kids are playing tag, some kids are on the swing, and some kids are playing hide-and-seek. Everyone seems to be having fun but wouldn't it be better if everyone played the same game together?
That is what Gleichschaltung is all about, making everyone do the same thing.
Hitler thought that Germany could become a more powerful country if everyone worked together and thought the same way. So he made rules that meant everyone had to be the same. All groups like schools, businesses, newspapers and even sports teams had to be controlled by the government.
It was like a giant game of Simon Says, where the government would say "Simon Says everyone has to be like this!" and everyone had to do exactly as they were told, otherwise they would get in trouble.
But just like you know that playing the same game all the time can get boring, many people in Germany didn't like being told what to do all the time. So while Gleichschaltung seemed like a good idea at first, in the end, it made a lot of people very unhappy.