Incredibly, it was Napoleon III who sent a French Force to enter Rome and protect Pope Pius IX thus restoring his temporal authority from Italian Republicans.
The unbelievable irony, is that Napoleonic France was the birthplace of all this atheistic revolutionary fervour... it was Napoleon I who imprisoned the Pope. Nobody would have guessed that turn of events. This was likely influenced thanks to a sizeable number of French Catholics due to the revival of the faith after the Revolution and downfall of Napoleon I such as those like St John Vianney (himself conscripted into Napoleon I armies, thankfully deserting or he would have been killed in the many Napoleonic wars) and St Catherine Laboure with the Miraculous Medal etc.
God Bless