I was playing as recently unified Japan in 1520s. I declared war on Brunei and pretty much every Indonesian country decided to war with me. The only ones in the entire region that didn't were Papua, and maybe three, one province countries. At Any rate, I steam rolled all of them within 5 years. Every province was "occupied". Every army was destroyed. So was every navy.
But there was a problem. No one would peace with me. Period. Not any of the one province states, not Maphajit (sp?) who owned about 50% of the provinces in the area. Not anyone. For another 5 years, I sent diplomat after diplomat. I tried vassalizing, I tried only taking one or two provinces, I tried just taking gold, I even tried white peace. Always rejected.
Also, it should be noted that every time I tried, it said "this offer is better than they are expecting..."
Anyway, after about 10 years of occupying all of Indonesia for nothing, the messages changed to "they will not accept this" even for white peace, or offering tribute... WTF? I waited about 20 more years (until 1555) and still, no one will peace and none of the occupied provinces got assimilated either.
Is this a bug, or are you just not allowed to conquer things as Japan, or what?