Board Thread:Warhammer 40k General Discussion/@comment-46.162.84.254-20130704080553/@comment-90.192.222.39-20170502214646

The Imperium is strongest because it is united. None of the other factions can say that except the Tau, who are much, much smaller yet can punch above their weight.

The Eldar unite from time to time but mostly stick to their craftworlds. Chaos isn't close to being united. The Necrons are legion but war among themselves. The Tyranid hive fleets attack each other on contact, well at least in 4th Ed Codex.