Al-Mustansir concluded a peace agreement to end the launched by Louis IX of France in 1270. Muhammad I al-Mustansir had been a vassal of the Kingdom of Sicily, but had shaken off his allegiance when King Manfred was overthrown by King Charles I.
The Mamluk sultan Baibars had been attacking the remnant of the Crusader states in Syria. Baibars had seized the opportunity after a war pitting the cities of Venice and Genoa against each other (1256–1260) had exhausted the Syrian ports that the two cities controlled.
By 1265 Baibars had captured Nazareth, Haifa, Toron, and Arsuf. These events led to Louis' call for a new crusade in 1267. Thus it was that Louis directed the against Tunis.
In 1270 Louis landed on the African coast in July. Much of the army became sick due to poor drinking water, and Louis himself died from a "flux in the stomach", one day after the arrival of Charles. His dying word was "Jerusalem." Charles proclaimed Louis' son Philip III the new king, but due to his youth Charles became the actual leader of the crusade.
Due to further diseases the siege of Tunis was abandoned on October 30 by an agreement with the al-Mustansir. After hearing of the death of Louis and the evacuation of the crusaders from Tunis, Sultan Baibars of Egypt cancelled his plan to send Egyptian troops to fight Louis in Tunis.