Greg Bear — The Forge of God
The 1990s present humanity with a dilemma when two groups of aliens arrive on Earth. The first invaders introduce themselves as altruistic ambassadors, but the second warn that their predecessors are actually unstoppable planet-eaters who will utterly destroy the world. The American president accepts this message as the ultimate judgment and calls for fervent prayers to appease the Forge of God. Meanwhile, military men plot to blow up spaceships, and both scientists and lay people help the second alien race preserve Earthly achievement.
Nominated for Nebula Award in 1987. Nominated for Hugo and Locus awards in 1988.