Shogun: Total War - The Mongol Invasion depicts a counterfactual historical narrative in which the Mongol Invasion of Japan under Kublai Khan - which was halted by a combination of logistical problems and storms that destroyed the Mongolian naval forces en route to Kyushu - actually transpired. Players are given a choice of playing through the Mongol Invasion Campaign as either the Hojo Clan (depicted as the ruling faction of the entire Japanese island chain) or the invading Mongolian forces.
Though the number of factions playable in this expansion is less than the base game, the strategic implications of playing either faction are considerable. The Hojo Clan have the "homefield advantage" throughout, are able to fall back into easily defensible fortresses within each province (each of which must be taken for the conquest of said province to be completed), and can use the entire island chain to their advantage by leveraging food supplies and man power to produce the maximum amount of men possible in a controlled, predictable system. The Mongolian forces, on the other hand, are beholden to what are at times frustratingly random armies of reinforcements sent from the Asian mainland and must deal with rebellion in conquered provinces. These weaknesses are mitigated by access to massive amounts of cavalry, strong auxiliary units, and relative freedom from the constraints of balancing a massive budget to keep their war machine going.