What one thing with the largest obstacle preventing unification of Italian states?

One of the largest obstacles preventing the unification of Italian states was the presence of foreign powers who had control over different regions of Italy. This included the Austrian Empire, the Kingdom of Sardinia, the Kingdom of Two Sicilies, the Papal States, and others. These foreign powers had conflicting interests and were reluctant to give up their control over their respective territories, making it difficult for the Italian states to unify.