4 ideas
Ibn al-Athir attributes the fall of Antioch and Jerusalem largely to rivalry among Seljuk emirs, competing atabegs, and the Fatimids of Egypt. Local rulers made truces, paid tribute, or allied with the Franks against Muslim rivals. Disunity recurs in the chronicle as an explanation for defeats, though recoveries such as Zengi's capture of Edessa in 1144 came before any single ruler held Aleppo, Mosul, Damascus, and Egypt.
Ibn al-Athir does not treat the Levantine invasion as a separate religious event. He opens it as the third stage of one Frankish advance across the Mediterranean: Toledo in Spain in 1085, then Sicily, then North Africa, then Syria. Seen this way, a local war becomes part of a long, multi-theater pattern of pressure, and the causes shift away from any single sermon or pilgrimage toward sustained expansion along the edges of the Islamic world.
After Hattin in 1187, Saladin took coastal towns by granting their garrisons safe conduct, and many released Franks gathered at Tyre, which Conrad of Montferrat held against Saladin's sieges. Ibn al-Athir blames Saladin's leniency and haste for letting the defeated concentrate in one defensible city that remained a Frankish base.
Ibn al-Athir credits Zengi and Nur al-Din with the counter-crusade and is noticeably harder on Saladin, who displaced the Zengids. These sympathies appear in his judgments about who deserves credit or blame, so readers should weigh those judgments separately from the events he reports.