There were various reasons for the ability of certain towns in Italy to establish a certain amount of self-government. The location of the maritime cities such as Genoa was able to benefit from the crusades making them powerful. This resulted in a knock on effect to the main inland towns and cities in the north due to increase in trade. This caused prosperity and growth, because of this and also because of certain socio-economic changes originating in the countryside, the cities and towns started to break away from the old feudal systems and look to a new order more beneficial to the newly formed city classes.
Their ability to consolidate this new government was due in part to the political upheaval which existed between state and church. This can be seen within the conflict of Henry IV and Gregory VII. The concept of self-government showed a major change in power within the Northern towns of Italy. The traditional feudal system was replaced by a commune, where all orders would share al rights and powers in common. This was implemented by an elected consul, where as before Kings such as the Lombards installed governors to rule, or at other times a powerful Archbishop would be the ruling power.
This can be seen in the rule of Archbishop Ansperte 868-81, (Ella Noyles p16) By the time of the 12th century, cities such as Milan had a government loosely based on the old Roman regime. This was a three tier system consisting of Captains the higher nobility and clergy; the vassals- the lower nobility and an increasing middle class formed of merchants and land leasers; and the common people such as the artisans and peasants. A consul was elected to govern the commune and was re-elected every year. This consul was elected by all three orders not just the elite.
This is what existed for self-government in the eleventh and twelfth century. The existence of self-government in the Northern Italian towns and cities was possible due to various reasons. In part it was location. The first crusades brought huge amounts of people and wealth into the maritime cities such as Genoa Pisa and also Venice. In consequence a great amount of trade was stimulated throughout Northern Italy and toward the inland towns and cities of Milan, Florence Ravenna and Pad ova to name a few. This also caused growth of people and trade.
Other causes can be seen in the city of Milan who became a virtual free state partly due to the weakness of the Holy Roman Emperor Henry IV when a minor and then been able ally itself with one sovereign such as Henry and then to another like Matilda, whilst in reality been independent of the both. However I believe one of the main reasons for these towns becoming self-governed was due to an economic and social change starting from the provinces. In the late tenth century, conditions had improved for the peasant class.
Rural life had become more secure due to building of town and castles defences, which helped to stop the Arab and Hungarian attacks. This, allied with the transformation of the Slaves into tenants helped the peasant population grow. This can be seen as Luzzatto (p69) suggests with new leases requiring new farms to be built and also with two or three families sharing holdings previously worked by just one. Also the once huge estates were leased out to farm, creating a new class of wealthy leaseholders.
These lease holders eventually demanded and ultimately received from the Emperor Conrad II, freedom from the restrictions on their land and also hereditary rights. This gave increased revenues which attracted them to the towns and the urban markets. These towns due to the increased trade with the maritime towns had also prospered thus attracting the over-populated peasants looking elsewhere for subsistence, which helped them change from rural to urban crafts, peasants to artisans.
The wealthy landowners and merchants saw that freedom from feudal overlords could be found within the cities. This was also true of the lower class, the popoli. These new socio-economic changes were vital to self-government and can be seen in the history of Milan, and its attempts to become a free state. In 1042, the vassals comprising of the lower nobility and minor clergy joined with the lower classes of artisans and serfs to revolt against the higher nobility under the leadership of a noble called Lanzone.
This resulted in a bloody civil war and the city being besieged by the Capitanis hired army for two years. This stale mate was finally broken by lanzones diplomacy. The three orders came to a compromise with all three orders sharing in government. Milan was able to keep this commune by giving token acts of recognition to the Emperors sovereignty. Also with the continued conflict between Gregory VII and Henry IV was able to prosper and become strong eventually leading them to implement an expansionist policy to dominate other cities such as Lodi.
Although, this expansionist outlook eventually caused the city to be destroyed by Frederick Babarossa in 1162. However this only consolidated the communes of Brescia, Bergamo, Cremona, Mantua, and Ferrara to form the Lombard League in 1167. This helped them to secure their independence, excluding a few hiccups until and past 1250. It is my belief that economic and social change within a certain time period were the main causes for the self government of the Northern Italian communes.
The changing climate within the countryside of over- populated peasants forced them into the cities, to look for new employment. They were joined by the newly formed class of land leasers who joined with the lower nobility and merchants. Their new wealth gave a desire to break with the old feudal system. They were able to do so by the prosperity of the cities through increased stimulation of trade which made the cities powerful and able to defend itself from a weakened sovereignty through an aggressive expansionist policy.