Anything involving interstellar travel, e.g. interstellar colonisation, interstellar war, is going to involve massive energy costs…

The percolation theory of Geoffrey Landis proposes that interstellar colonisation may be possible, yet so difficult that even highly advanced civilisations sometimes decide not to attempt it. Landis also argues that advanced non-colonising civilisations may hinder the expansion of civilisations that want to colonise, since it would not be possible to colonise a planet if an advanced civilisation is already there.

Extending the argument a little, if space colonisation is difficult but possible, the same may be true of interstellar war. The costs could be massive enough that even the most paranoid civilisation would not or could not destroy every life-bearing planet it detects.

Yet if interstellar warfare is possible at all, an advanced non-colonising civilisation might well feel threatened by someone else’s attempt to colonise nearby uninhabited planets. They might consider attacking a young, struggling colony before it grows into a monster.

The possibility of this happening would make interstellar colonisation still more difficult…