Fascinating thread. 
Before this crazy election, what were the big historical (like recent historical 
) political divides in Italy based on? Religion, region, class mostly? Anyone care to give some specifics to this American poster and European-politics n00b?
In essence, the Italian political landscape has been shaped by more than a millennium of Romanic-Germanic conflict, starting with the fall of the (west-) Roman empire at the hands of Odoaker, and the
Lombard conquest of Italy in 568. By the end of the first millennium, Northern Italy was reasonably firmly integrated into the Holy Roman Empire of German Nation (Otto the Great's wife Adelheid of Burgundy was Queen of Italy, her grandson Otto III ruled the empire from Northern Italy).
Subsequent power struggle between Emperor and Pope deepened the rift between much of imperial-controlled Northern Italy, and the Papal State in the centre. The struggle between
Guelfs (papal) and Ghibellines (emperor) went on for most of the middle age, and is still remembered today, as is signified by the Lega Nord picking its name in allusion to the 12th century Guelfish Lombard League. Dario Fo noted in the early 1980s that Guelf cities tended to vote communist / socialist, while Ghibelline cities voted Christian democratic (it would be interesting to check whether that still holds true today).
The Pope-Emperor conflict reached its height under Emperor Frederick II, who was born and raised in Sicily, and ruled for most of the time from Apulia, thus putting these two regions, as well as much of Southern Italy, firmly into the Ghibelline camp.
So, essentially, what we are seeing today is Guelf areas (former papal territories, Tuscany) and the former city republics of Venice and Genua voting red (Genua actually switched over to MSS), and the Ghibelline territories in the north and south voting blue. Trento- Alto Adige, with its strong German minority, is a special case - here the major German-speaking party allied with PD.
The only surprises here are Torino and some parts of South Italy, especially the Basilicata, voting red as well - maybe someone with a bit more background on local issues and history can help explaining this.
