  We give a nonperturbative derivation of the Bethe--Salpeter equation based on
the Feynman--Schwinger path integral representation of the one--particle
propagator in an external field. We apply the method to the quark--antiquark
system in scalar QCD and obtain a confining BS equation assuming the Wilson
area law in the straight line approximation. The result is strictly related to
the relativistic flux tube model and to the $q \bar{q}$ semirelativistic
potential.
