In response to threats from the Republic of Venice and the Kingdom of Naples, Duke Ludovico Sforza of Milan invited France and Spain into Italy to protect Milan. The First Italian War began when Charles VIII, the French King, invaded Italy in 1494 in response to Sforza's request for aid. He took Naples but was driven out by Spain after Italy and Spain created an alliance against him. 

Britannica, The Editors of Encyclopaedia. “Italian Wars.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 4 Mar. 2016, www.britannica.com/event/Italian-Wars.