  We discuss the instability of the Veneziano-Yankielowicz effective action (or
its supersymmetric ground-state) with respect to higher order derivative terms.
As such terms must be present in an effective action, the V-Y action alone
cannot describe the dynamics of SYM consistently. We introduce an extension of
this action, where all instabilities are removed by means of a much richer
structure of the Kaehler potential. We demonstrate that the dominant
contributions to the effective potential are determined by the non-holomorphic
part of the action and we prove that the non-perturbative ground-state can be
equipped with stable dynamics. Making an expansion near the resulting
ground-state to second order in the derivatives never leads back to the result
by Veneziano and Yankielowicz. As a consequence new dynamical effects arise,
which are interpreted as the formation of massive states in the boson sector
(glueballs) and are accompanied by dynamical supersymmetry breaking. As this
regime of the dynamics is not captured by standard semi-classical analysis
(instantons etc.), our results do not contradict these calculations but
investigate the physics of the system beyond these approximations.
