Italy was Roman though. Or rather by making Italy Roman (to such an extent that other Italians would be willing to fight a war just for the right to be treated as other Romans) was basically what enabled their success by giving them a huge pool of manpower (and most importantly of people who had a vested interest in the success of the Roman state). Other ancient states like Athens were inherently exclusionary which put a hard limit on their power projection capacity since they depended on fickle allied or subjugated states to fight their wars.