I've been thinking of this for a while.
What if the Sengoku jidai ends in an uneasy peace/stalemate between several major clans? Let's say whoever gets central Japan (including Kyoto) fell a bit short in defeating the far-flung regional clans (like the Shimazu, Mori, Date, etc.) and decided to negotiate a settlement, where the regional clan will recognize the authority in Kyoto, at least nominally, in exchange for some degree of independence.
How long can the uneasy peace last before somebody gets itchy to go for war again? What if that setting lasted? Any other effects?