The Romans are misjudged. They conquered and subdued but many of the places they conquered and subdued became Rome. Gaul, Iberia, Britain, North Africa, Italy, they fit this pattern. And those places fought to remain Rome, losing in the end.

The benefits to being Roman were enormous. The pattern of town construction in Celtic areas and Gaul I believe show this clearly. Before the Romans, hilltop fortified towns. During the Roman times, towns in the valleys where the water was. After the Romans, back to hilltop fortified towns.

The Romans did pay at the end when the empire was weak. But that was when the empire was weak. When it was strong, for the most part, they killed you if you bothered them. Which leads us to how did the empire get so weak. Goldsworthy argues that it essentially destroyed itself through continuous civil war over centuries. I think that is a good argument. Others have different ideas.