The Collaborative International Dictionary of English v.0.48:

Buncombe \Bun"combe\, Bunkum \Bun"kum\, n. [Buncombe a county of
   North Carolina.]
   Speech-making for the gratification of constituents, or to
   gain public applause; flattering talk for a selfish purpose;
   anything said for mere show. [Cant or Slang, U.S.]
   [1913 Webster]

         All that flourish about right of search was bunkum --
         all that brag about hanging your Canada sheriff was
         bunkum . . . slavery speeches are all bunkum.
                                                  --Haliburton.
   [1913 Webster]

   To speak for Buncombe, to speak for mere show, or
      popularly.
      [1913 Webster]

   Note: "The phrase originated near the close of the debate on
         the famous `Missouri Question,' in the 16th Congress.
         It was then used by Felix Walker -- a na["i]ve old
         mountaineer, who resided at Waynesville, in Haywood,
         the most western country of North Carolina, near the
         border of the adjacent county of Buncombe, which formed
         part of his district. The old man rose to speak, while
         the house was impatiently calling for the `Question,'
         and several members gathered round him, begging him to
         desist. He persevered, however, for a while, declaring
         that the people of his district expected it, and that
         he was bound to `make a speech for Buncombe.'" --W.
         Darlington.
         [1913 Webster]