The Collaborative International Dictionary of English v.0.48:

League \League\, v. i. [imp. & p. p. Leagued; p. pr. & vb. n.
   Leaguing.] [Cf. F. se liguer. See 2d League.]
   To unite in a league or confederacy; to combine for mutual
   support; to confederate. --South.
   [1913 Webster]