Lets say in 1168 King Amaleric of Jerusalem does a better coordinated effort with the Byzantines (Manuel) to take Egypt.
1. Fatimid Egypt very weak
2. An alliance signed to take Egypt
3. Byz fleet takes 6 months (vs 3 months supply)
4. Manuel himself leads Byz instead of testy admiral
5. Manuel brings Vargarians (3500 of the 6000), half of the western and eastern Tagmata (10,000) and 5,000 mercs. --- vs just the fleet
6. Crusaders bring their forces as the brought in real time
7. Dalmatia is put under siege, Alexandra taken by side group (3000 )
8. Dalmatia falls through siege and final assault with extra Byz troops available.
9. Egypt taken with a Joint rule and split of profits
10. Extra income from Egypt (80% of Saladin future income) is now supporting the efforts of the Crusaders ( 20% to Byz - which is used to hire more mercs and support more Byz troops to retake Anatolia) (80% goes to support more troops for the crusaders)
11. Future is based upon garrisons of Egypt(with new funding), doubling the forces of the Crusaders and attacking and taking the interior cities of middle east (Damascus, Aleppo, Homs), which would increase the crusader states revenue (from cities plus keeping their origional lands protected from raids) allowing for more military spending.
12. The support of the Crusader (wealthier) states and the Byz (wealthier) would allow for the reconquest of Anatolia.
Fourth Crusader invasion, 1168–1169[edit]
At this point in time the Crusaders should have focused on strengthening their position against Syria, but instead Amalric was tempted by the
Hospitaller Knights to attack Egypt and take it. Manuel Komnenos received the idea well. The alliance was still being finalized when Amalric launched a quick attack against
Bilbeis in 1168, massacring the population. Shawar appealed to Damascus and Shirkuh returned. When faced with an imminent attack by Amalric, Shawar ordered the burning of his own capital city,
Fustat. Shirkuh then fought off Amalric, killed the untrustworthy Shawar, and seized power. Shirkuh himself died two months later and his nephew, Saladin took power as regent.
At Damietta, the Byzantine-Crusader alliance materialized into a siege of the port. The Crusaders attacked late while the Byzantines, after three months abandoned the siege. In 1171, after the death of Caliph Al-Adid, Saladin proclaimed himself Sultan while the Crusaders under Amalric were forced to retreat, having lost many men due to disease and warfare. The Knights Hospitaller became bankrupt after the operation but made a quick recovery financially. The same could not be said for the Kingdom.
WIkii
https://en.wikipedia.org/wiki/Crusader_invasions_of_Egypt