Which factor most slowed down the unification of Italy?

The Kingdom of the Two Sicilies was a large and powerful state in southern Italy that was ruled by the Bourbon dynasty. The Bourbons were fiercely opposed to Italian unification, and they were able to use their military and diplomatic power to block unification efforts for many years.

The Kingdom of the Two Sicilies was eventually defeated by the Piedmont-Sardinian army in 1860, and Italy was unified in 1861. However, the unification process would not have been possible without the military and diplomatic support of France. France was interested in weakening Austria, which was the main protector of the Kingdom of the Two Sicilies, and it was willing to support Italian unification in order to achieve this goal.

In conclusion, the resistance of the Kingdom of the Two Sicilies was the main factor that slowed down the unification of Italy. However, the unification process would not have been possible without the military and diplomatic support of France.