Italy
Savoy
By the end of the 15th century Savoy was a significant power in northern Italy, but at the start of our period it was quite small and insignificant. All of northwestern Italy was comprised of tiny city-states and principalities, and Savoy's expansion gobbled these up. The expansion was not uninterrupted, though, as it constantly had to contend with the Visconti in Milan, with the French, and with strong cities like Geneva. Most of Savoy lay north of the Alps, but it also held Piedmont, which was centered at Turin. Piedmont was controlled by the Angevins early in the century but was gradually acquired by Savoy.
One of the more famous rulers of Savoy was Amadeus VI (1343-1383), known as the "Green Count" because of his armor. I won't go further into the geo-political history of Savoy because it's so complicated. You can generally view it as expanding in importance and possessions over the course of the 14th century and into the 15th century. Towards the end of the 15th century, Savoy stabilized, having run up against stronger powers. On the other hand, if you want a taste of a genuinely medieval principality, Savoy would be a good study. The governments of France or England or the Empire were in many ways atypical; Savoy was in many ways typical.
Savoy did not play much of a role in the politics of the peninsula. It's true that Savoy was a sometime member of the Italian League in the later 15th century, but mainly as a me-too participant, not as a leader. The duchy was preoccupied with its own internal matters, and with dealing with its powerful neighbors.
Amadeus VIII (d. 1451) gained the title of duke in 1416.