  We examine the low-energy dynamics of four-dimensional supersymmetric gauge
theories and calculate the values of the gluino condensate for all simple gauge
groups. By initially compactifying the theory on a cylinder we are able to
perform calculations in a controlled weakly-coupled way for small radius. The
dominant contributions to the path integral on the cylinder arise from magnetic
monopoles which play the role of instanton constituents. We find that the
semi-classically generated superpotential of the theory is the affine Toda
potential for an associated twisted affine algebra. We determine the
supersymmetric vacua and calculate the values of the gluino condensate. The
number of supersymmetric vacua is equal to c_2, the dual Coxeter number, and in
each vacuum the monopoles carry a fraction 1/c_2 of topological charge. As the
results are independent of the radius of the circle, they are also valid in the
strong coupling regime where the theory becomes decompactified. In this way we
obtain values for the gluino condensate which for the classical gauge groups
agree with previously known ``weak coupling instanton'' expressions (but not
with the ``strong coupling instanton'' calculations). This detailed agreement
provides further evidence in favour of the recently advocated resolution of the
the gluino condensate puzzle. We also make explicit predictions for the gluino
condensate for the exceptional groups.
