I wondered about this.. I was playing Mori and I saw Chosekbe as a potential target, so I scouted the area and only showed 1 full stack and a half stack. The first castle was an easy target then came the full stack defeated them at cost of my own next turn (the half stack I saw had to be at least 2-3 turns away) here comes another full stack they beat me at heavy casualties to themselves and take their land back. I have a another half stack standing by so I launch another assault the next turn and their at full strength I beat them and a smaller stack ....here comes another Full stack with full stack of allies so I say if you want that bad you can keep it lol. End of story..I retreat and regroup with 2 full Stacks! and case your wondering how I was able to manage all these units is with 34000 Kouku and making 8000 a turn
I kind of like the idea since I like fighting waves (some times) but it get tedious think.. Mongol hordes in M2TW. I also hate the Idea at the same time because like many have said its cheating, they could at least make it like an event were if your beating them real bad a message pops up saying Enemy Samurai fear players expansion and raise up against you (or something).