We determine the exact global structure of the moduli space of N=2
supersymmetric SO(n) and \USp(2n) gauge theories with matter
hypermultiplets in the fundamental representations, using the
non-renormalization theorem for the Higgs branches and the exact solutions for
the Coulomb branches. By adding an (N=2)--breaking mass term for the
adjoint chiral field and varying the mass, the N=2 theories can be made to
flow to either an ``electric'' N=1 supersymmetric QCD or its N=1 dual
``magnetic'' version. We thus obtain a derivation of the N=1 dualities of
Seiberg.Comment: 20 pages, harvmac (b