What the reserves can—and can’t—do
A military force is not an abstraction, nor does it spring into existence ex nihilo. A military force is the product of three interlocking sets of factors: national objectives, available forms of military power, and political constraints upon the use of that power. A military force is built from the “top down,” in the sense that its overall structure is (or should be) determined by the imperatives of national survival and strategy. It is also built from the “bottom up,” ill the sense that its components must utilize certain weapons, technologies, and human beings, while forgoing others. And finally, a military force is built from the “outside in,” shaped (in democracies, at least) as much by non-military factors as by strategies and weapons and possible foes.