Dr. Manhattan is a power that committed atrocities in the name of the U.S. government, and thus even with the United States being blatantly afraid of him there will always be strong thoughts that all of this is manipulation on the part of the U.S. government and Dr. Manhattan. That alone prevents actual peace and…

It's not merely an alien attack. It doesn't even have to be an alien attack, per se. That giant telepathic squid-like monster is specifically and pointedly a nod to Lovecraft. That is the very image of an Elder God is ever there was one.