I've recently become interested in the city-states of medieval Italy (Venice, Mantua, the Papal States, Naples, Savoy, Genoa, etc) and their politics, development, and wars. Mostly I'm interested in the wars and how the states came to be.

I know a lot of Roman history, but very little of Italy after Rome was conquered by the barbarians. Can anyone recommend a relatively easy book on the Italian Wars that makes sense of the various city-states, political players, and their conflicts?