[m4rtink]

Once a civilization reaches a certain tech level, it can do interstellar travel & by the time you find about it due to light speed delay, it might be far too late to strike - not to mention what size & tech level they might be by the point your first strike wave arrives given the time scales of sub light travel.

So it might be better to use the tried and tested terrestrial nuclear MAD doctrine & rather doe careful diplomacy with any newcomers, like a bunch of psychos each having a full arsenal of planet killing weapons (because that's what any sufficiently advanced civilization is).

In short - rather than Dark Forrest I imagine a harmonious if not utopic galaxy teaming with varied life that is on the first glance peaceful and cooperating.

With the occasional bunch of start systems evaporating once in a while, but we don't talk about those.