Quote Originally Posted by Sakkura
In the Roman Republic there was the further incentive of Roman citizenship and electability. Perhaps even some "nationalistic" motivations?
So there was some difference, although how big it was probably differed a lot around the Mediterranean world.
That only applies to auxilleries, and only in the Principate after 25 years service. In essence Watchamn is correct about the post-Marian Legions. They were mercenaries and would fight for whoever paid them and had a decent chance of winning.