The growing European powers in lieu of having a control over Mediterranean sea had conquered various Italian states because of its strategic location, and basically there was no state or an entity called Italy. But enters the great ruler of the times, Napoleon, goes on an Italian expedition. Conquers all the small states. Unites Italy on the social and political front to ease his own administration, the people of Italy get a taste of unification which led to the economic development. Italy happy.
However, there comes a twist in the plot, France sees the fall of Napoleon. Come Vienna Congress Convention. Restores old order, makes some Papal states ( Pope Head), gives some states to France, and majority states go to Austria, including important ones like Lombardy and Venice.
Italians shell shocked. Disappointed. Nationalist aspirations shattered. Enters hero Mazzini. Motivates people for unification of Italy. But no external support, Austria too powerful, couldn’t gather all Italy support.
Meanwhile, Cavour a chancellor of state Sardinia, which had a liberal king (Victor Emmanuel) sees the need for unification, inspired by Mazzini adopts foreign diplomacy policy. Supports France and Britain in Crimean wars. They win, and he gets background support from Napoleon III from the treaty of Plombieres by offering huge gifts to Napoleon.
Cavour now provokes Austria, fights with them, defeats them in initial few battles, Austria sensing the support from Napoleon threatens him, Napoleon pulls back, the war ended abruptly, but Cavour gets them to sign Truce of Villafranca , and gets Lombardy, Venice still remains with Austria.
In the smaller states like Tuscany, Parma, Romagna, they conduct plebiscites gets majority support of the people, (remember inspiration of Mazzini) so local kings overthrown and these states are taken into Italy.
Enters the Scene Garibaldi, who strengthens the army, goes on fighting spree, brings back Sicily and Naples by force, wins the support of People.
Victor Emmanuel goes himself and gets Papal States.
Remain now Rome and Venice.Garibaldi goes to Bismarck for support, Bismarck fights with Austria in 1866 over the Schleswig and Holstein incident. Austria lost, Italy gets Venice.
Remains Rome, which is with France, Garibaldi seeks support of Bismarck, Franco Prussian wars, France humiliated, Italian army captures Rome.
All states back under the Sardinian King, with Rome as capital, Italian states unified, Mazzini’s dream fulfilled in 1870.