As the Second Italian War raged, Louis XII's knights pressed southward into Naples to confirm the king's claim to the Italian throne. He had taken Ferdinand II of Spain as an ally, offering to divide the spoils once Louis dominated Italy. Ferdinand had agreed, but once Naples was taken, the two bickered over which lands would go to whom. Aragon and France turned on each other, each taking up allies and mercenaries from the locals.
They returned to the French army, and word of the fight worked its way up to the Duke of Nemours. He and his advisers discerned the effectiveness of the small arms, just as they had for the long range cannon, of which the French had much more than the Spanish. Over the next months, he encouraged his pike-wielding Swiss to emulate the Spanish Coronelias, which fought with mixed pikes, swords, and arquebuses.
In late April, Nemours moved on the Spanish at Cerignola. The French outnumbered them 32,000 to 8,000 and had twice as many cannon, but the Spanish "El Gran Capitán" Gonzalo Fernández de Córdoba had expertly fortified the high ground with trenches, walls, and stakes. Heavy Spanish artillery fire broke up the initial French charges, and Nemours first planned an attack on the right flank against arquebusiers. However, as he recalled the effectiveness of the arquebus against a knight from the tournament a couple of months before, he decided on a new strategy. War had changed, and to be victorious, the French army would have to adapt beyond artillery.
Nemours moved his artillery and began pounding the Spanish infantry. When they seemed softened, he moved forward the Swiss and assaulted, taking the first volley from the arquebuses with an exchange of fire. Before the Spanish could reload, the French knights charged past the Swiss and stormed the trench. The Swiss followed after the breach, and the numbers of the French army overwhelmed the Spanish defenders. While the French took massive casualties, the Spanish were thoroughly defeated, and expert commander Córdoba was captured.
The next year, the Louis signed the Treaty of Lyon with Ferdinand, securing French control over mainland Italy. Spain still held Sicily, but Louis had built a league with Venice and the Papal States that would dominate Italy and, perhaps more importantly, the growing trade with the East. During the rebuilding of Italy, Francis I instituted imperialistic laws to dominate the Italian banking, shifting the financial center of Europe from northern Italy to Paris. Portugal flourished with trade from India, and Spain grew wealthy on gold from the New World, and France launched its own expeditions to dominate Africa and the Mediterranean, interrupting the expansion of the Ottomans, as well as colonizing much of what would become North America.
During the nationalistic revolutions toward the end of the Age of Enlightenment, the Italians would rally to unify themselves in revolt against France in 1798, creating a new state and key player in Europe.
In reality, the Disfida di Barletta did not involve firearms, but the Battle of Cerignola did. The French knights were defeated by the Italians, and, at Cerignola, they were defeated by the Spanish Coronelías. The French would again be defeated at Garigliano, leading to the Treaty of Lyon in which Louis XII would cede control of southern Italy to Spain. The peninsula was divided and would not be united until 1861.