Honestly, this was a load of shit. Every single country that rebelled against Britannia got rid of all of their military and relied solely on the Black Knights for their defense...then sent them off on a crusade to liberate Japan.
While the Black Knights are off liberating Japan, every other country will get steamrolled because they have no military. Black Knights get Japan, every other country gets fucked due to their dumbass decision that no real country would make.
Oh wait, this is anime. Japan alone can save the world.