Suppose that the Romans only go so far as the edge of the Italic peninsula and the various Greek and Punic colonies around the Mediterranean Sea remain intact. What could happen that would contain the spread of the Romans, assuming that Rome is not eventually destroyed?
I thought about the spread of populations from a resource conservation point of view, in the sense that going far from one's homeland would require great amounts of time and resources (food, shelter, materials for tools, etc.) But I want a more coherent and sensible description ·· perhaps involving alternative developments of specific events such as the Pyrrhic War that could lead to different outcomes in the long term.
Any ideas for how a sensible alternate timeline can work given the assumptions in the first paragraph?