For me attacking Jomon would have been much better.. for you too I think since we only have one province where we meet, both castles there so no way to take lands easily.. If I hadn't had problems with Jomon you'd have lost though.. since I only use 50 % of my resources on you. 
Now I'm having some problems expanding cus I have two persons to war with
You could turn on Jomon in the south, I'd give you a new NAP and then I could take on Jomon for real near our castles...
let me know 

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