In the aftermath of Crimean War two catholic powers of Europe made a deal...
Basically 1850/60s austro-french alliance. Austria loose "Upper Italy" but acquire Danubian principalities and, after war with Prussia, finally reclaim Silesia, while Saxony reclaims its lands loose after Napoleonic wars and Wittelsbachs exchanged Pfalz for Vestphalia. France get Savoy, Nice and Belgium (Leo gets spanish throne).
Francis of Modena was compensate by Luxembourg (since he is childless, after his death it will became part of France), Robert of Parma was promoted to grand duke of Tuscany, while former grand duke, Leopold of Habsburg, became duke of Posen. Russia was "compensate" by southern Bessarabia and easternmost chunk of Galizia.
But there is one more secret treaty between Napoleon, Franz Joseph... and Leopold of Posen. How could protectors of papal state just overcome oppression of their brethren in faith...?