  Motivated by the recent D-brane constructions of world-volume monopoles and
instantons, we study the supersymmetric SU(N) Yang-Mills theory on $S^1 \times
R^{3+1}$, spontaneously broken by a Wilson loop. In addition to the usual N-1
fundamental monopoles, the N-th BPS monopole appears from the Kaluza-Klein
sector. When all N monopoles are present, net magnetic charge vanishes and the
solution can be reinterpreted as a Wilson-loop instanton of unit Pontryagin
number. The instanton/multi-monopole moduli space is explicitly constructed,
and seen to be identical to a Coulomb phase moduli space of a U(1)^N gauge
theory in 2+1 dimensions related to Kronheimer's gauge theory of SU(N) type.
This extends the results by Intriligator and Seiberg to the finite couplings
that, in the infrared limit of Kronheimer's theory, the Coulomb phase
parameterizes a centered SU(N) instanton. We also elaborate on the case of
restored SU(N) symmetry.
