I wonder how long that strategy will work. Eventually society will reach a new "equilibrium" but how many less defended societies will succumb to the starving hordes before that happens.

I quote "equilibrium" because social structures never stop changing. What I mean is a relatively stable situation where most of the world is not invading the rest of the world. Our present situation is that the larger portion of the population is not invading the rest, though the present trend seems to be in the wrong direction.