The Collaborative International Dictionary of English v.0.48:

federalize \fed"er*al*ize\, v. t. [imp. & p. p. Federalized;
   p. pr. & vb. n. Federalizing.] [Cf. F. f['e]d['e]raliser.]
   To unite in compact, as different States; to confederate for
   political purposes; to unite by or under the Federal
   Constitution. --Barlow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

federalize
    v 1: unite on a federal basis or band together as a league; "The
         country was federated after the civil war" [syn:
         federate, federalize, federalise]
    2: put under the control and authority of a federal government
       [syn: federalize, federalise]
    3: enter into a league for a common purpose; "The republics
       federated to become the Soviet Union" [syn: federate,
       federalize, federalise]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "federalize":
   affiliate, ally, associate, band together, be in cahoots, bunch,
   bunch up, cabal, cement a union, centralize, club, club together,
   come together, confederate, consociate, conspire, couple, federate,
   gang, gang up, go in partners, go in partnership, hook up with,
   join forces, join fortunes with, join together, join up with,
   join with, league, marry, organize, pair, pair off, partner,
   stand together, stand up with, team up with, team with,
   throw in with, tie in with, tie up with, unionize, unite with,
   wed