John Rambo fought in the Vietnam War, where he earned multiple commendations, including the Congressional Medal of Honor. However, he, like many unfortunate souls, has many scars as a result of his time there. Some are physical, some are not.
Article source: https://www.cinemablend.com/news/2480437/everything-you-need-to-remember-about-the-rambo-franchise-before-last-blood