Hip-hop has long been infatuated with its own history. “You love to hear the story, again and again/ Of how it all got started, way back when” declared the Juice Crew’s MC Shan at the beginning of his 1986 classic “The Bridge,” a song made when recorded rap music was a mere 7 years old. “The Bridge” was a landmark recording for a number of reasons: For starters, Shan’s producer, DJ Marley Marl, used his Korg SDD sampler to lift drum hits from the Honey Drippers’ 1973 “Impeach the President,” one of the earliest uses of a sampler on a hip-hop record. (“Impeach the President” is now one of the two or three most exalted breaks in all of hip-hop.) But it also reached the ears of a young MC from the Bronx named Kris Parker, aka KRS-One, who heard those opening lines as Shan claiming (wrongly) that hip-hop had started out in Queensbridge. In response, KRS and his crew, Boogie Down Productions, released “South Bronx,” an obsessively detailed tour through that borough’s hip-hop history, kicking off what would come to be known as “the Bridge Wars.” Thus, one of the music’s earliest and most storied wax battles was born, at least superficially, out of a historiographical dispute.