He told his followers to render to Caesar what was Caesar's. But nothing belonged to Caesar thereabouts, did it.
It was a reply to his enemies, not followers.
He said it after pointing out Ceasar's head on a coin.

it can hardly be said, almost from the outset of Christianity, that non-violence was central to its creed.
At the outset, as again today, Christians were the victims of violence.
Inevitably, in 2000 years of history, mistakes were made.
And...?