Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150406151006/@comment-3416287-20150408050416

The Imperium on its own has a hard time defeating even one hive fleet. If the races of the galaxy came to an agreement somehow they would be able to easily defeat a hive fleet, but a galactic alliance is like 99.99% impossible. Plus, the fact that tyranids have attacked the glaxy from several different directions suggests that they have eaten all the nearby galaxies. If the tyranids consumed even a single galaxy's biomatter, then they would be near impossible to stop. If they consumed several galaxies worth of biomatter than the only thing people could do is hide in the webway, flee to the warp, or hibernate like necrons and hope there is enough left to rebuild.

The solution is not firepower, as not a single race has enough firepower to defeat the tyranids, and the races of the galaxy aren't likely to work together. Unconventional tactics are required. In the Ciaphas Cain novel "The Greater Good", a group of tech adepts learned how to cut the psychic link between tyranids and the hive mind, thus turning them into beasts, but they only achieved that in a laboratory and on a small scale.