They were already getting tribute from Gaul. He didn't have to slaughter them, he did it because he was tired of dealing with small insurrections in an area he viewed well below him. He was a man of ambition who didn't want to be stuck in Gaul having to babysit the area all the time.
I said Caesar wasn’t perfect. Moral standards then were different then now. You don’t think Pompey and others did fucked up shit too?
And I really don’t give a shit if Caesar was breaking the “law” set in place by Roman bureaucrats. He did what was necessary.
They were already getting tribute from Gaul. He didn't have to slaughter them, he did it because he was tired of dealing with small insurrections in an area he viewed well below him. He was a man of ambition who didn't want to be stuck in Gaul having to babysit the area all the time.