Ok, seems like people don't like the idea that things are difficult to do ... there are other difficulty levels and you don't have to complete the game, only attempt to.

And it's not a linear game, you may try to expand in any way you wish, if catholic excom your way through with no thought to religion, god forbid you try a peaceful campaign defending your borders. Role play is not everyones cup of tea but you can still make a decision to play the game in a certain way if you wish.

In my campaign (first one) I think I have about 60 turns left to take 12 regions and Jerusalem (have antioch and adana in the middle east), I may well do it, especially if I can get a vassal or 2 but the damn mongols came south and took the whole of the levant.

Why is it necessary to complete the objective if you can't? There is not a specific advantage to doing so as you unlock the nations you conquer as you do so, not through victory conditions.