The Collaborative International Dictionary of English v.0.48:

Subvene \Sub*vene"\, v. i. [imp. & p. p. Subvened; p. pr. &
   vb. n. Subvening.] [Pref. sub- + L. venire to come. See
   Subvention.]
   To come under, as a support or stay; to happen.
   [1913 Webster]

         A future state must needs subvene to prevent the whole
         edifice from falling into ruin.          --Bp.
                                                  Warburton.
   [1913 Webster]