On 1 January 1188, Saladin held a war council where a withdrawal from Tripoli was agreed. Pope Gregory VIII called for a Third Crusade against the Muslims in early 1189. Frederick Barbarossa of the Holy Roman Empire, Philip Augustus of France, and Richard the Lionheart of England formed an alliance to reconquer Jerusalem. Meanwhile, the Crusaders and the Ayyubids fought near Acre that year and were joined by the reinforcements from Europe. From 1189 to 1191, Acre was besieged by the Crusaders, and despite initial Muslim successes, it fell to Richard's forces. A massacre of 2,700 Muslim inhabitants ensued, and the Crusaders then planned to take Ascalon in the south. The Crusaders, now under the unified command of Richard, defeated Saladin at the Battle of Arsuf, allowing for the Crusader conquest of Jaffa and much of coastal Palestine, but they were unable to recover the interior regions. Instead, Richard signed a treaty with Saladin in 1192, restoring the Kingdom of Jerusalem to a coastal strip between Jaffa and Beirut. It was the last major war effort of Saladin's career, as he died the next year, in 1193. Rather than establishing a centralized empire, Saladin had established hereditary ownership throughout his lands, dividing his empire among his kinsmen, with family members presiding over semi-autonomous fiefs and principalities. Although these princes ("emirs") owed allegiance to the Ayyubid sultan, they maintained relative independence in their own territories. Upon Saladin's death, az-Zahir took Aleppo from al-Adil per the arrangement and al-Aziz Uthman held Cairo, while his eldest son, al-Afdal retained Damascus, which also included Palestine and much of Mount Lebanon. Al-Adil then acquired al-Jazira (Upper Mesopotamia), where he held the Zengids of Mosul at bay. In 1193, Mas'ud of Mosul joined forces with Zangi II of Sinjar and together the Zengid coalition moved to conquer al-Jazira. However, before any major results could be achieved, Mas'ud fell ill and returned to Mosul, and al-Adil then compelled Zangi to make a quick peace before the Zengids suffered territorial losses at the hands of the Ayyubids. Al-Adil's son al-Mu'azzam took possession of Karak and Transjordan. Soon, however, Saladin's sons squabbled over the division of the empire.