This is ancient Japanese warfare
From 1180 A.D. to 1185 A.D.
Do not miss Inarmo's in game description, it not only sets the game up, but is a vary good story :)
To read more about the Genpei War check out the Wiki
Scene from the Genpei war
For our Japanese guests you can visit Inarmo's website
His other mission is Tokyo Railway Wars