  This is the first of a sequence of papers that address the non-perturbative
origin of the central, and spin-dependent forces between quarks. Its main
thrust is a focus on meson spectroscopy in the center of mass frame. We suggest
a "dense instanton ensemble" model for the QCD vacuum, to explain the
interquark forces in mesons, from quarkonia to heavy-light and light-light
ones, to the extent it is possible. The sequels will show how to export these
interactions to the light front, and derive the corresponding Hamiltonians and
mesonic wavefunctions.
