The term originated in Oakland to describe both Northern and Southern Californian Raider fans shortly after the team's return from Los Angeles to the Bay Area. The term first represented the whole of California being the Raider Nation, but was quickly expanded because there are Raider fans world wide.
In fact, adding the term "nation" to a sports team is an original idea from the Oakland Raider fans who are the most loyal, loud and proud fans in all of sports. Therefore, pretender "nations" like the Red Sox "Nation" are made up of fraudulent fans who plagarize the Raiders.
Fans of the San Diego Limp Bolts, the Denver Jackasses and the Kansas City Cheaps have nothing on the Raider Nation.