AHC: Early Italian Unific

  Assuming you mean after the collapse of the western Roman empire then possibly in the 6th century.  If either Justinian supports Belisarius and Italy is reunited under the eastern empire within a couple of years and without the devastation of the 'Gothic' wars.  Or possibly even Belisarius is persuaded to accept the Italian throne, which apparently the Goths offered him and then, possibly aided by distractions of the eastern empire in the Balkans and/or with the Persians quickly secures a de-facto independence.  [Although given Belisarius's famous loyalty to Justinian this would be a big change.]

  Either way the region is strong enough to defeat later incursions by Lombard's and other groups and develops its economy, then - in the former case - later breaks away from the eastern empire as an independent state.  Of course such a powerful Italy with imperial traditions could end up seeking to secure other parts of the former empire which either leads to overstretch if unsuccessful or a state that isn't Italian as we would think of it.

  There might be chances later on but you really need it before Charlemagne's establishment of what became the HRE as that tied norther Italy into Germany and other areas while other areas stayed either Byzantium or Muslim controlled until the Norman conquests - which since the Norman state in S Italy and its successors were outside the HRE mean the peninsula was divided.  Also what happens with the Papacy as its going to be a massive power elements and is likely to clash with any secular state in Italy just as it did with assorted HRE rulers.