Rambo is a PTSD-laden ‘Nam veteran, drifting over flyover country and getting mistreated by everyone he finds.
Some small town sheriff arrests him on trumped up charges and tortures him until he snaps and holes up on an abandoned mine, not before ambushing all the deputies one by one.
The National Guard is summoned, with bazookas, but they are locals with guns. Dozens of guys with military grade weaponry don’t stand a chance against one former Green Beret.
After he is presumed dead, he doubles back to find and kill the evil sheriff. His former Army CO who came to help out listens to his grievances and stops more bloodshed, leading him to turn himself in and restoring some peace.
This was based on a book and many character development scenes were cut. The sheriff was supposed to be a Korean veteran and resents those young whippersnappers from Vietnam. Here, he turns into the standard ignorant small town sheriff on a mission to trample on the downtrodden.
For a Rambo film this is quite introspective and non violent. He only kills the sheriff in the entire film, everyone else survives. A guy falls out of a helicopter because he takes out the seat belt.