Blood Meridian belongs to the genre of historical fiction. McCarthy's story takes place against the backdrop of 19th-century America. Manifest Destiny—or the notion that the United States is destined to expand westward throughout North America, displacing the native peoples in order to spread American values—is central to the story, and McCarthy weaves a tale of violence and imperialism within this moment in history.
In fact, McCarthy draws from a primary source in writing Blood Meridian—My Confession: Recollections of a Rogue, by Samuel Chamberlain. My Confession details, among other things, the life of John Joel Glanton and the Glanton Gang, and McCarthy draws on this source in creating characters like John Joel Glanton and Judge Holden, both of whom have the same names as their real-life counterparts from Chamberlain's memoir.
By drawing from the historical record, McCarthy grounds his tale of gore and violence. In fact, Blood Meridian includes frequent allusions to other stories, including the Bible and Milton's epic poem Paradise Lost. By intertwining references to memoir and fiction, McCarthy makes the unreal real and visa versa, ending with a novel that has itself been described as neo-biblical.
Blood Meridian is heavily inspired by westerns, which was new for McCarthy as an author at the time of Blood Meridian's publication but is evident in many of his later works, from No Country for Old Men to The Border Trilogy. McCarthy actually traveled across the South to visit the geographical places he would then describe in great detail. McCarthy himself grew up in Knoxville, Tennessee, where the novel's closest thing to a protagonist, the kid, is born. Nevertheless, the story is far from autobiographical and belongs firmly in the genre of historical fiction.