The Battle of Fornovo
The first major battle of the Italian Wars occurred at Fornovo, near the city of Parma. After the French army had systematically swept through the Kingdom of Naples and would return northward to France, the coalition of powers that would be dubbed the League of Venice, decided to stop him. Gathering a force of around 20000 men, the League enlisted the help of Francesco II, Marquess of Mantua, a hardened Condottiero, to lead this army against the French.
As the security of the Italian states was in jeopardy, in contrast to the relatively small French army (and as some pointed out, it wasn't even France's full strength) the League forces had to decisively outnumber the French. However, they were divided in what to do, as Charles VIII declared his intention of seeking safe passage through northern Italy. Eventually, with his army's supplies running low, Charles decided to join battle.
The League took positions on the right side of the Taro river, whilst the French took to the left side of the River. Dividing his army into three sections, with the largest commanded by Charles himself, the French army was protected by artillery.
Francesco began his attack by making his light cavalry harass the French front line, which failed due to the inhospitable terrain. His main battle plan was to distract the French with his first two lines and flank with the rear; although this would work, the battle soon descended into a bloody melee when the French baggage train was set upon by League cavalrymen. Eventually, the French were forced to retreat, their plunder from Naples ultimately lost.
Although the League would lose twice as many men as the French, the latter would retreat, as Charles licked his wounds. Nevertheless, he stewed, and he would be back[1]...
Back in Castile, joyful news greets the court: Archduchess Margaret of Austria is pregnant[2]. The Trastamara dynasty would be secure, and doubly so if the child were to be male.
[1] In OTL he would not return to Italy, seeing as he died after hitting his head on a door lintel after a game of jeu de paume. TTL, that accident is butterflied away.
[2] Butterflies a-flapping. In OTL Margaret gave birth to a stillborn girl shortly after John died.