  We derive a set of constraints on soliton solutions using geometric
deformations, and transformations by internal symmetries with space-dependent
parameters. We show that Derrick's theorem and a more complete set of
constraints due to Manton are special cases of these deformation constraints
(DC). We demonstrate also that known soliton solutions obey the DC, and extract
novel results by applying the constraints to systems of D-branes, taking into
account both Dirac-Born-Infeld and Wess-Zumino actions, and examining cases
with and without D-brane gauge fields. We also determine a relation with the
Hamiltonian constraint for gravitational systems, and discuss configurations of
finite extent, like Wilson lines.
