Once upon a time, in a country called France, there was a man named Alfred Dreyfus. He was a soldier in the army and was very good at his job. But one day, he was accused of doing something very bad - he was accused of spying for another country.
Even though there was not much evidence against him, people started to believe that he was guilty, and he was sent to prison. People were very angry with him, and some even hated him just because they thought he was a traitor.
But there were other people who thought that he was innocent and that he was being unfairly punished. They started investigating the case and found out that there was no real evidence against him.
The people who believed that Dreyfus was innocent were called "Dreyfusards," and the people who believed he was guilty were called "Anti-Dreyfusards." They even had big protests and fights about it.
Finally, after a long and difficult process, it was proven that Dreyfus was actually innocent. The real spy was caught, and Dreyfus was freed from prison.
This whole situation became known as the "Dreyfus Affair," and it was a very important moment in French history. It showed how important it is to have a fair trial and not to judge people just because of rumors or prejudices.