how can I outmatch Korea?

I'm playing as japan in 1608 and I've conquered a lot of territory now with 1000 development, while Korea with no more than like 200 somehow has a way bigger military than me with 135 regiments against my 110 (I've already built alot of regimental camps) so i don't get how I can conquor them alone at this point when they also have level 4 fourts, i don't have any allies that can help but they don't have any either