Stallone portrays a seriously burned-out Vietnam vet who long ago went native. He runs an African Queen-style boat on a river in northern Thailand, a river that flows from Burma. Rambo gets hired, against his better judgment, to take a group of medical missionaries into eastern Burma. Then he gets hired to take a group of mercs to the same spot to attempt a rescue. Finally Rambo gets to rescue everybody who's still alive, many are not.
One thing I like about the film is that it is set in an area - Burma or Myanmar - where the government suppression of minority tribes portrayed in the film actually happens. I prefer films that are somewhat realistic, geopolitically.
Of course, the film shows this conflict entirely from the viewpoint of the tribes, the politically correct view. The Burmese believe they are dealing with secessionist rebels and the the anti-government tribes which support them.
Who's right? The tribes are the underdog, but the territory they occupy is legitimately part of Burma. You decide.