All the movie sequels after 'First Blood' are hallucinations and delusions suffered by Rambo after his breakdown.It explains the difference in tone and genre between the films. Rambo has retreated into his own mind and created a world where violence is the norm and his skills still have some value.
The canon ending to 'First Blood' was the deleted one, where Trautman kills Rambo. The next movies are Rambo's personal Valhalla.John Rambo is a born soldier. Fighting for the sake of another is the best thing he can do. He never resorted to violence per pure spite, per hatred or pride: All his fights, the pain and the sorrow were for the sake of another people, and for his country. He died figthing, but he wouldn't ever hurt a friend, like Trautman. So he earned his eternal reward: To fight, for a good cause: To rescue the inocents from the cruel oppresors.
It's not a delusion, and it's not his personal Hell: It's a reward, and it's a duty to the world: The prize for being Rambo, is that you'll become Rambo