Dreyfus Affair
The affair divided France into people who thought Dreyfus really was a spy and people who thought he was innocent.  Many of those who thought Dreyfus was a spy hated Jews and believed that he was a criminal because he was a Jew, and that a Jew could not be a good Frenchman; this belief is called anti-Semitism.  Others thought that the army could not be questioned. The other side believed that an innocent man should not be imprisoned, and feared that Dreyfus's enemies were also enemies of France.