imperialism in antiquity

[Epictetus]

Have you tried WV Harris's groundbreaking War and Imperialism in Republican Rome? You can read the introduction in the link and see if it fits what you are looking for. It is a bit dated, originally published in 1979 I think, but it really started a good academic discussion on this issue. Even very recently books have been published trying to refute Harris, such as Eckstein's 2006 Mediterranean Anarchy, Interstate War, and the Rise of Rome.