"Karen" doesn't have the same meaning in that part of the world as it does here. The Karens are a minority group in Burma that has long been at odds with the Burmese government. Civil war and repression have driven many Karens to Thailand, where hundreds of thousands now live.
Warfare between the would be conquerers in Yangon and the Karens and Kachins has been going on for a lo-o-o-o-ng time, centuries, perhaps?