>>96569851That's oversimplifying a complicated situation.
The Senate was afraid of the power Caesar acquired through his conquest of Gaul, both the actual value of the massive new province and also the popularity at home.
So the Senate declared that Caesar had executed an illegal war in the name of Rome and he has to come back home immediately to face his crimes.
Caesar, who was sitting pretty with his legions at the time, went "Hmmm.. Yeah, I don't trust you. How about I come back home with my giant trained and experienced army and we can talk about what's legal and what's not".
So he marched his army home to find that most of the Senate had run off.
The ensuing war was Caesar trying to unify Rome again. He was, by all accounts, extremely merciful in doing so. Turned out to be a mistake in the end.
