Flask up attack full on the Troops either side of the Officer Base, then head inside and take the base, once taken make your way around the map towards the center and kill Troops till fully flasked.
Now make your way to the tower Base and capture it. continue around towards the north, killing as you go and go capture the Captains base. Exit to the east and go back to the center and capture the 100 Troops Base,
Now K.O untill you have 1000+ K.Os (try and get an Attack x2), once you hit 1000 3 Captains will appear (each has Hyper Armor). defeat them.
Your general will now appear outside the enemy Supply Base. lead them to the Box (marked above) and hope for an Imperial Seal.