If you check ths script in the campaign_script file, you will see that you need some more settlements:
Hobbiton, Michel Delving, Lognbottom, Bree, Staddle, Barrow-Downs, Amon Sûl. Annùminas, Fornost, Hoarwell, Tharbad, Coldfells.
And you need Aragorn alive!
But you own most of these settlements anyway...
Oh and the order you complete the requirements doesnt mather. I startet with the alliance with Gondor.
Code:
monitor_event FactionTurnStart FactionType turks
and not IsFactionAIControlled
and I_LocalFaction turks
and I_CharacterExists strider1 -> Aragorn
and DiplomaticStanceFromFaction sicily = Allied -> Ally with Gondor
and I_SettlementOwner Shire = turks
and I_SettlementOwner Bywater = turks
and I_SettlementOwner Southfarthing = turks
and I_SettlementOwner Bree = turks
and I_SettlementOwner Staddle = turks
and I_SettlementOwner Cardolan = turks
and I_SettlementOwner Weather-Hills = turks
and I_SettlementOwner Lake_Evendim = turks
and I_SettlementOwner Arthedain = turks
and I_SettlementOwner Mitheithel = turks
and I_SettlementOwner Lone-lands = turks ;Tharbad
and I_SettlementOwner Ettenmoors = turks
and FactionBuildingExists >= house_of_kings
and I_CompareCounter union_offered = 0