The Founding of a Great Nation
Before the year of 1747, Italy was a mess. It was divided between citystates and powers who played an intricate game of diplomacy. It was a powderkeg, and in 1747, someone lit a match.
On 1/18/1747, Austria marched on Sardinia-Piedmont, sparking a war that would last barely a year. As Austria brought the rest of Italy under its firm control, it looked elsewhere. It saw France, struggling to deal with people calling for the end of the monarchy. As it mobilized its army to counter the Austrian threat, France collapsed into anarchy, the entire army deserting. Within days, Austria brought Southern France completely under control. Only fear of overextenstion and rebels in Italy saved France from complete annexation.
Unfortunately for Austria, the inhabitants of Venezia soon revolted. With most of the Austro-Hungarian military might tied up in France, the Venetians had a clear route to Vienna. As they marched on Austria's homeland, rebels from all over Italy swarmed to their army. The Venetian army's ranks swelled, and before long the army numbered over 350,000, and approaching Vienna quickly.
As the army reached Vienna, they immediately assaulted the walls, battering it with artillary and swarming over the ramparts. The army marched to the city center, proclaiming Austria dead, the HRE disbanded. As soon as they heard this, the Greeks marched into Hungary, crushing the last remnants of Austrian resistance.
When the dust settled, Italy had been freed, Austria conquered and South France occupied but without a strong leadership body, it was all sure to come crashing down. The Venetians were the obvious choice, and they decided to create a republic, to prevent further rebellion. They obviously went with their own style, the Merchant Republic, and thus Italia was born.
Note: this was obviously alt-history, but so is this game...