France--under Napoleon III--sent troops to defend the papacy in 1850, largely to appease French Catholics. These troops helped the papacy maintain control of Rome and ended the short-lived Roman Republic. When the Papal States were attacked in 1860 the French troops largely stayed out of the fighting until it came near Rome itself, then they defeated a group of volunteers led by Garibaldi. From 1860-70 they were the main reason that the papacy kept control over Rome, but the French troops were withdrawn when France lost the Franco-Prussian war. The new Italian state defeated the remaining papal defenders in rapid order and seized Rome.

So, there was a bit of pragmatic defense of the Papal States from France, but that was ended by the Franco-Prussian war. There were also volunteers that flocked to the papal banner from a number of countries, but not with their nation's support.