Simplify the following text for a Grade 9 native English-speaking person.
Original: Affiliated with the NWA once again , the WWWF was renamed to World Wrestling Federation ( WWF ) in 1979 , and after conclusively ending its affiliation with the NWA in 1983 , the championship became known as the WWF World Heavyweight Championship and later simply as the WWF Championship by the 1990s .
Simplified: During this time , the title was called the World Wrestling Federation ( WWF ) Heavyweight Championship . It became known as the WWF World Heavyweight Championship when the promotion left the NWA in 1983 .