In 1500, Louis XII made an agreement with Ferdinand II on dividing the Kingdom of Naples, as Frederick IV was removed from the Neapolitan throne. This was known as the Treaty of Grenada. This decision was heavily criticized by influential figures such as Niccolo Machiavelli, whose opinion was embraced by many of Italy’s citizens as well. When Charles V came into power in 1519, he gained more of a reputation in Italy, as he joined Spain together with the Holy Roman Empire.
The war began in 1536 between Charles V and Francis I of France commenced upon the death of Francesco II Sforza, the duke of Milan. Sforza had no children and died of a long and painful illness in 1535. Because he had no heirs, Francesco’s dynasty was brought to an end by Charles V, whose niece, Christina of Denmark, was Francesco’s wife. There were no protests when Charles V took over the Duchy of Milan from either the people or other Italian states. This shift in power marked a new era for France, as Jean de la Foret was brought in as an ambassador to the Ottoman Empire, a territory coveted for its wide range of goods and large amount of power. Foret and Francis I secured an alliance with the Ottoman Empire, giving France a strong army, ready to attack targets such as Marseille and Piedmont, areas close to the Italian province of Genoa.
When Charles's son Philip inherited the duchy, Francis invaded Italy. Philippe de Chabot, a French general, led his army into Piedmont in March 1536, and proceeded to capture Turin the following month, but he failed to seize Milan. In response, Charles invaded Provence, a region of France, advancing to Aix-en-Provence, and took Aix in August 1536 but his movement was halted by the French Army blocking routes to Marseilles. Afterwards, Charles withdrew to Spain rather than attacking the heavily fortified Avignon. There is also a story that French troops deliberately left over-ripe fruit on the trees in an attempt to give Charles's troops dysentery.
While Charles V was busy fighting for territory in France, he lost focus on events taking place in Italy. Francis I’s armies received massive reinforcements in Piedmont in terms of generals, troops, and horses on a march headed for Genoa. France had secured an alliance with the Ottoman Empire in 1536 through the diplomatic efforts of Jean de La Forêt, France's ambassador to the Ottoman Empire. A Franco-Turkish fleet was stationed in Marseille by the end of 1536, threatening Genoa, by planning to attack simultaneously with the French troops marching on land towards the city. Unfortunately for the French and Ottomans, when they arrived in Genoa in August 1536 the defenses of the city had been recently reinforced. Instead, the troops marched onto Piedmont, capturing many towns there. In 1537 Barbarossa raided the Italian coast and laid a siege at Corfu, although this provided only limited assistance to the French.