I mean, romans created a huge empire but they originated in the italian peninsula, a land not really rich in resources of any kind not even that much fertile meanwhile northern europe was rich of any resource ancient empires needed, wood, metals, the fertile north european plain, a lot of rivers, a lot of wild animals to hunt and a lot of cultures with no natural barrier able to condivide their technologies and prosper but they never prospered nor created a technologically advanced empire.
Although the conditions for empire-building are by no means universal and I don't think your question has an easy, or clear, answer, I do think you have a number of misconceived ideas about Italy. Even though the surroundings of Rome were alternatively hilly and swampy, Italy itself is extremely fertile, from the volcanic soil in Campania and Sicily to the low floodplains of the River Po and the flatlands of Apulia. The ancient Greeks believed the goddess Ceres lived in Sicily, so absurdly fertile was the island.
The mediterranean was intrinsically densely urbanized, and is a basin that is particularly favorable to the formation of cities: there are numerous seafaring trade routes (until the advent of steam power, sea travel was much faster than land-based travel) and high agricultural fertility levels which can support mercantile populations that aren't farming. These things really do culminate in Italy; it's easy to see why in the urbanized Italian peninsula would develop customs and institutions where citizens of interconnected cities would be guaranteed certain rights and freedoms favorable to urbanization and guarantee the rule of law, even in the context of an empire (the Italian Social Wars come to mind as a prime example).
I'm less well-versed in the Greek world, but I believe that the Aegean sea and Peloponnesian Peninsula were also very inductive to urbanization, albeit agriculturally less fertile than Italy.