daphne you beat me to it! Sicilians and Calabrese still use dialects which are totally different to Italian- and that Northern Italians just couldn't comprehend. In fact the whole of the South, including Sicily, was 'Sicily- then the centre was ther papal States, and the North a whole array of small countries, including Tuscany, and Sardinia in the NE, including the island of, Lombardia and Tyrol, etc.
As you say, much more than language- different ethnic groups and history altogether- but not separated by an obvious dividing barrier like Offa's Dike or Adrian's wall.