The Collaborative International Dictionary of English v.0.48:

Centralism \Cen"tral*ism\, n.
   1. The state or condition of being central; the combination
      of several parts into one whole; centralization.
      [1913 Webster]

   2. The system by which power is centralized, as in a
      government.
      [1913 Webster] centralist

WordNet (r) 3.0 (2006):

centralism
    n 1: the political policy of concentrating power in a central
         organization