May be u don't know the concept of a supply line ...

a supply line is needed for a fielding army that is invading an enemy territory , it can support by pillaging and foraging of course but not for too long time , so a supply line is needed especially in crossing desertical places .... also , the Holy land isn't a desert but a fertile land , apart some places it is quite lush .....

and the concept of a supply line applies to a moving army , not when it conquered already a territory , wich in that case can freely abuse of the local resources to an extent tough ....