  Domain walls in supersymmetric Yang-Mills are BPS configurations which
preserve two supercharges of the parent theory and so their tensions are known
exactly. On the other hand, they have been described as D-branes for the
confining string. This leads to a description of their collective dynamics in
terms of a 2+1 -dimensional gauge theory with two supersymmetries and a
Chern-Simons term. We show that this open string description can capture the
qualitative behaviour of the forces between the domain walls for an arbitrary
configuration of n walls at leading order in 1/N, extending earlier
calculations for two walls. The potential admits a supersymmetric bound state
when the n walls are all coincident and asymptotes to a constant at large
separation with an n dependence which agrees perfectly with the exact tension
formula.
