Italy
Guelf and Ghibelline
In this on-going conflict, no outsider ruled the Italian city-states, but everyone wanted them as allies. Various popes and emperors had made lavish grants to various cities in an attempt to gain support. The practical result was that most Italian cities were free to pursue their own destiny, especially under a weak emperor.
Political conflict took on the language of the imperial struggle. Among the cities, this one was Guelf while that one was Ghibelline. Even after the actual conflict was long over, the terms were used, though now they simply described two warring factions within the various cities. Every Ghibelline city had its Guelf faction, and vice versa.
The local factions could ally with like factions in other towns; and so foreign policy become entangled in local politics. Opposition was thus next to treason, which helps account for the violence of suppression; conversely, victory over neighbors almost always meant a political purge. Also, state politics frequently smacked of personal vendetta.
Emperor Henry VII
The language became embedded in Italian politics. Even people at the time spoke in terms of Guelf and Ghibelline. The conflict was given fresh impetus when Henry VII entered Italy in 1310. It technically wasn't an invasion. Emperors had to travel to Rome to be crowned there. This meant they had to travel through northern Italy, and that meant they travelled through the Kingdom of Italy, a collection of principalities and cities that had formed a kingdom back in Charlemagne's day but which had long been effectively independent. Henry decided he would re-exert imperial influence there.
Henry's arrival in Italy at once forced every north Italian power to choose sides. If they intended to resist Henry, they naturally turned to the pope for support and were called Guelf. If they cooperated with Henry, they were naturally called Ghibelline. The conflict with the Hohenstaufen created the two great Italian factions, but Henry's descent into Italy sealed them in place.
This, then, was the scene in 1300, when our course begins. Italy was divided into three major regions, each of which was divided further into a patchwork of states and cities. Coloring all relations was the underlying struggle between popes and emperors. The only way to get an appreciation for any of this is simply to dive into the swirling waters. We'll move from south to north, so we begin with Naples and Sicily.