Overview
During the time of the Renaissance Italy was decided into smaller, "states." Though there were multiple small states in Italy, Milan, Venice, Florence, the Papal States and Naples managed to rule most of the peninsula. The Northern most part of the country was ruled by the Republic of Venice and the Duchy of Milan. The Republic of Venice was known for its ability to keep a stable government in the Renaissance as well as cultivate a drive to acquire more land. The Duchy of Milan underwent some treason early on in the Renaissance by Francesco Sforza, a high ranking condottieri. He turned on and took Milan effectively becoming the new Duke. This happened in 1447 and shortly afterwards, with the help of the Visconti family, former rulers, he managed to increase taxation, thereby increasing the income of the state and created a, "centralized territorial state."
Republic of Florence
While the city of Venice is known to be a beautiful and prosperous city, at least in the Renaissance, Florence was actually considered the cultural center of the Renaissance for a good time. The city was said to be controlled by a Republican Government, but for most of the 15th century the merchant family of the Medici controlled the politics and ran the city behind the scenes. However the fact that a rich merchant family ran the city while pretending that Florence was run by a republican government wasn't out of the ordinary. In fact many other merchant oligarchies had done exactly the same in the past.
Papal States
The Papal States dominated central Italy and had once been under the sole authority of the Pope, but had gained freedom by the time of the Renaissance. This was due to the fact that many of the Popes recently before the Renaissance had taken up residence in Avignon, France. Their absence had given cities like Bologna, Ferrera and Urbino the chance to free themselves from the Papal Authority and they did. So for a good portion of the Renaissance one of the Popes' main concerns was trying to regain control of the original Papal States.
Kingdom of Naples
The Kingdom of Naples seemed tucked away in the Southern most part of Italy during the Renaissance and it had few cultural glories during that time. Naples was fought over for a good time by the French and the Aragonese. Eventually the Aragonese won out and controlled Naples, though it seemed all for nought. While they did control the state they didn't do well for themselves. The majority of their Kingdom was poverty stricken and it was almost always ruled by corrupt kings.