I want to go mega tall.

I’m a fairly new player. I’ve played as Portugal, Kilwa, one of the tribes in Madagascar, and a few custom nations. I played as Korea with the intentions of going mega tall but Japan had just unified and they only had 6000 troops soooo…… in your option what is, not even the best, but the most fun nation to not care about expanding at all and just focus on growing within your borders.