A

Italian city states were a political phenomenon of small independent states mainly on the central and northern Italian peninsula between the 9th and 15th centuries. There were city states of Florence, Pisa, Lucca, Siena, and Ancona in central Italy, and Salerno, Amalfi, Bari, Naples, and Trani were in the south of Rome.

Colosseum in Rome.
Fig.1 Colosseum in Rome

Explanation:

The main prerequisite for the emergence of Italian city-states was the fall of the Western Roman Empire. It turned out that Rome was not able to rule such a vast territory, which they managed to conquer. The Italian cities, as the main heirs to the Roman culture, tried to adhere to the usual norms of life. However, soon many city-states became so strong that they were able to defend independence.
The first city-states appeared in the 11th century, becoming the result of the struggle of Apennine Peninsula settlements with Holy Roman Empire troops. An alliance to fight the common enemy was created at the initiative of Milan, Ferrara, Parma, Lodi, and Piacenza. It was called the Lombard League and consisted of settlements, which became the first independent city-states (Milan, Verona, Parma, and Bologna, etc.).
Maritime republics, the largest of which were Venice and Genoa, played than essential role in that era. They had a considerable advantage due to access to the sea, in particular, the opportunity to establish trade relations with Indian, Muslim, African countries. Sea cities built their fleets to protect and develop trade, allowing them to enter the political arena. For instance, they could participate in the Crusades, as well as discover colonies in the waters of the Mediterranean and Black Seas. In the 15th century, the Italian republics were powerful enough to begin redivision, primarily for the mastery of trade routes. They spared neither strength nor money to pay for the hired commanders of military units, which mainly consisted of foreigners. Large cities subjugated the weaker ones; in particular, Venice appropriated a massive territory in the north of Italy.