[maxerickson]

The most likely shape of interstellar war is lasergrams that say "We hate you" (but here is some harvestable energy...).

The next most likely is probably relativistic projectiles, which are dangerous in proportion to the energy required to send them (i.e., they aren't that likely a threat).

Direct invasions of civilizations that can shape the matter of an entire solar system seem pretty much destined to failure (I guess you could come in on a ship built from an entire solar system, but I wonder if you are war mongering at that point).