Question

Why might the Italian city-states have resisted the exploration around the world?

Answer 1

One reason why Italian city-states may have resisted the exploration around the world would be that "The discovery of new trade routes to the east threatened the city-state's control over that trade," since for most of the 1400s the Italians dominated the spice trade (along with the Muslims). 

Answer 2

The discovery of new trade routes to the east threatened the city-state's control over that trade