As with many European countries during this period, Italy was not governed by a solitary royal family. This was partly because the end of the Hohenstaufen empire left a power vacuum in Italy at the start of the fourteenth century.
The majority of cities at this time were under the authority of a Lord or aristocratic family. A large percentage of these Lords were native to their respective cities but it was not uncommon for an outsider (even one from another country) to seize control. Naples was governed between 1309-1343 by King Robert who was from a branch of the house of Anjou, while Sicily was ruled by a member of the house of Aragon. The succession of Roberts heir, Joanna, was contested by King Louis of Hungary. The issue was not resolved until Ladislas of Hungary stamped his authority on the city in 1404. His massive power and influence forced the northern cities into forming a coalition against him.
As there were no official army, Lords maintained their positions by using hired militants to the defend the city or take over other cities.. A useful example of this is Genoa which was economically, but not politically, powerful. The internal conflict amongst rival nobles presented an easy target for the Viconti family of Milan who intermitently took control before the Genoese Lords fought back.
As well as Milan, Florence and Venice were the other main cities in Northern Italy but the latter two often acted as an alliance during conflict with Milan which has been described as the "most powerful mainalan city of northern Italy". Florence differed from other cities because it was governed by merchant rather than just a single Lord. Like Milan, Florence also had an aggressive territorial policy and had previously bought, or taken by force, several smaller town in northern Italy including Arezso, Leghorn and Pisa.
However, the threat Milan posed to other cities ended with the death of Gianaleazzo Visconti in the early fifteenth century. By the middle of the century, both Florence (led by Cosimo de Medici-1454) and Milan were moving towards reconciliation and alliance which ended conflict in Italy until the end of the century.