I beg your pardon, but rome in 270 BC had the manpower to defeat Carthage! The Successors were the only ones that could compare themselves with Carthage at the time and rome beated carthage in a war that started 6 years later. I'm not saying that rome was the strongest one, just one of the strongest. Pyrhus attacked them but he was repelled. He had an extremly well equieped army but failed to brake Rome's rising power. They're resources were huge, that's why i consider them to be one of the top countries at the time.

P.S. I'm faaaaaaaaaaaaaaaaaaar from being a Rome fanboy