Play as either an Arabian or European Lord against seven allied opponents of the opposite faction.
Set your identity to Arabian or European before you begin to get the full effect, then when the game starts you'll see you're restricted to troops and buildings belonging to either side.
For example, set your identity to Arabian and play 'An Arabian Alone'. You will only have a mercenary tent to recruit from and certain 'European buildings' will be unavailable. Select seven allied European AI Lord opponents, give them a gold advantage and experience the Arabian stand against the invading infidel!
Alternatively, set your identity to European and play 'A European Alone'. Certain 'Arabian buildings' will be unavailable. Select seven allied Arabian AI Lord opponents, give them a gold advantage and truly feel like a European invader in a strange and inhospitable land!