The end of the Roman Republic. Caesar
Gaius Julius Caesar crosses the Rubicon, triumphs, and declares himself dictator. In 44 BC he is killed in the Senate.
The philosophical cause
Cicero — All his life Cicero wrote that the Republic was the only form of government worthy of a human being. He tried to stop Caesar with words.
Caesar is killed, but the Republic does not revive. Augustus becomes the first emperor. Cicero is executed — his head put on display in the forum.