The difference between Vargr migratory and Aslan expansionary is that for the Aslan it's expected and prepared for, and that instinct is probably triggered by known and expected environmental and socio political economic factors.
Suppression of that instinct probably is easier for humans, though social expectations probably would force them to participate in those practices, in order to maintain their positions in the Aslan hierarchy, because, we do believe in expand or die, it's just that we can decide in where our personal interests and futures lie.
It's likely the expeditions are funded to export their problems to the frontiers, or they'll probably fall into civil war, interclan or intraclan.
It's interesting the term range is used in the title; for the Vargr, they are probably territorial, and have hunting ranges. It's when they come to the conclusion that they can't defend them, or it's not worth the effort, that they move to somewhere else.