Hip-hop's first holy war began, fittingly, with a perceived act of blasphemy. MC Shan and Marley Marl's "The Bridge" was a celebration of their Queensbridge neighborhood. But to KRS-One and the Boogie Down Productions crew it was an affront to the South Bronx, the birthplace of hip-hop. BDP released "South Bronx" in retaliation, and the resulting back-and-forth spawned some incredible music, including the oft-imitated BDP classic "The Bridge Is Over."

Back then, a rapper's only recourse was to pour all of his energies into records antagonizing his enemies, and for two years that's all BDP, Marley Marl's Juice Crew, and their allies did. Two decades later, "The Bridge Is Over" remains a stunning track: Even as his lyrical references fade into obscurity, KRS-One's effortless delivery exudes the kind of hyper-confident swagger that would become the sine qua non of good hip-hop.