In today's world, when we think of class conflict, we tend to think of the poor in conflict with the rich. In the Italian Renaissance, however, the more important class conflict was between the merchant class (many of whom were quite wealthy) and the nobility. This conflict helped to shape the Renaissance.
There are at least two ways in which this is true. During this time, the merchant class was getting richer and more important as cities' economies came to be based on trade. This led them to demand political power to go with their economic power. In cases like that of Florence, this led to the creation of a republic and eventually the rise to power of merchant families like the Medici.
This class conflict helped to lead to some of the artistic achievements of the Renaissance as well. Some members of the merchant class patronized the arts as a way of showing their wealth and asserting their right to be more important in society. By doing so, they helped to promote the arts that are so identified with the Italian Renaissance.