The Republic of Rome in 1849 survives by defeating the French army. A stable republic is established and built up, and an effective army is trained by Garibaldi.
Over the next few years, The Republic's army will conquer the smaller states in north central Italy, and unite with Lombardi in Milan.
In the south, they attack and conquer the Two Sicilies, defeating a Spanish Army in the process.
When Prussia attacks Austria, the Republic joins on Prussia's side and attacks and takes Venice. Napoleon III joins Austria's side and attacks the Romans along with Piedmont. After Austria is defeated at Koniggratz, Prussia attacks and defeats France, who abruptly pull out of Italy to defend Paris. The Piedmontese are defeated by the Romans under the direct command of Garibaldi, and Savoy is incorporated into the Republic.
France is defeated by the Prussians and Napoleon is deposed. Prussia unifies Germany but does not annex Alsace-Lorraine.
With Italy unified under the Republic of the Romans, the state centralizes itself and asserts its authority. With an effective, well-trained, and well-led army, a centralized, democratic, and secular state, and the beginnings of an industrial base, Italy becomes a world power, able to effectively participate in Europe's conflicts to its benefit.