the main plot of rdr1 is basically the fbi kidnaps abigail and jack, and forces john to turn in/kill the rest of the gang; i don’t remember what caused the falling out between john and the gang. john does so, the fbi returns his family, and they go back to live out their days in their house that you built at the end of red dead 2. happy ending
and then the game actually ends with the fbi randomly showing up at the house and murdering john by shooting him approximately 100 times in a dead eye shootout you can’t win. abigail and jack bury john. “Bury Me Not on the Lone Prairie” plays in the background
you do get a post-game quest where a teenage jack hunts down the two main fbi agents and kills them