You can unlock them manually by following these instructions:

Quote Originally Posted by frogbeastegg
To do this you can either complete a campaign (on any difficutly, long or short setting) with one of the five starting factions, or you can edit the preferences file. To do this open your Sega/M2TW folder/data\world\maps\campaign\imperial_campaign, find the file called "descr_strat" and open it with wordpad. Now find the section which says
Code:
campaign      imperial_campaign
playable
   england
   france
   hre
   spain
   venice
end
unlockable
   sicily
   milan
   scotland
   byzantium
   russia
   moors
   turks
   egypt
   denmark
   portugal
   poland
   hungary
end
nonplayable
   papal_states
   aztecs
   mongols
   timurids
   slave
end
Change it so it reads
Code:
campaign      imperial_campaign
playable
   england
   france
   hre
   spain
   venice
   sicily
   milan
   scotland
   byzantium
   russia
   moors
   turks
   egypt
   denmark
   portugal
   poland
   hungary
end
nonplayable
   papal_states
   aztecs
   mongols
   timurids
   slave
end