i think they meant alien as in like unknown not as aliens. Thats why they said seemingly, because to the player, the enemy is seemingly unknown. Now the question is who is this alien force? France. JK
on subject though, im betting this new force is japan. Seeing it is the pacific, japan would make since (if im getting my history right) and the reason there 'alien' is probably because of the change in tactics the Japanese used from the german/american tactics. Cant wait though