What best explains the success of the first crusade?

Overview : The success of the First Crusade can be best explained with multiple factors contributing, some with more effect than others. These factors include Spiritual devotion, Military tactics, strong leadership and muslim disunity. (For a 'best explains' question, you can either start with what you think 'best explains', or finish with it. I think its best to finish with it because then you can plan accordingly, knowing your 'answer' will be well signposted. It might not be best to jump straight in with 'The disunity of the muslims best explains', because some of your other points may be lacking and the examiner will think you've thrown them in without sufficient knowledge. The alternative is to consistently signpost that the point you've made 'was a contributing factor' but 'does not best explain', with this method you can make your argument at the start or the end.)So, a paragraph for this question could look something like - (Point) 'The disunity of the Muslims best explains the success of the First Crusade'(Evidence) 'This is because in the preceding twenty years before the Council at Piacenza, Jerusalem had changed hands between the muslim factions four times'(Analysis) 'One simply has to look at the disaster of the Second Crusade, as well as the failure of the Third (and largest) to see that once the Muslims had unified under Saladin (and the Jihad), the first crusaders would not have been nearly as successful.(Evidence 2) 'The siege of Antioch shows how beneficial the disunity of the muslims was to the First Crusaders. The Crusade would have been destroyed if Kerbogha of Mosul had not been abandoned by Ridwan and Duqaq (of Aleppo and Damascus repectively).'(Analysis 2) 'If the Two brothers (Ridwan and Duqaq) had put aside their personal ambition and fought alongside Kerbogha then the First Crusade would have been destroyed outright. By the end of the siege of Antioch one in seven of the crusaders was dying of disease, showing that they would not have had the numbers to fight off all three forces.'(Link) 'The evidence provided by the second and third crusade failures, and the very conspicuous disunity at Antioch shows why the disunity of the Muslims best explains the success of the First Crusade.'