>>213556027
It's more of a Half-Life style Resonance Cascade even than a "nuke." By all accounts, it looks like the Americans were researching interdimensional mechanics at the Institute for Spatial Studies, and accidentally made contact with something... and that "something" was malevolent.
That's how it would look to the rest of the world. It would actually specifically implicate Adrian in this case, because the Institute for Spatial Studies was a Veidt-funded laboratory.
The fact that Dr. Manhattan mysteriously goes missing shortly afterwards has even more dire implications, because when your most powerful weapon is suddenly gone, it's entirely possible to assume the worst and that the squid could be more powerful than Dr. Manhattan; or that the event that summoned the squid could also have possibly killed Dr. Manhattan. No way to tell, because nobody but Adrian knows what happened to Dr. Manhattan, and he's not coming back.
So essentially, if you don't have reader-privileged information about the squid incursion, it looks like some science experiment gone horribly wrong, and it's not unreasonable to point the finger at Americans for trying to mess with forces beyond their control or understanding (because they've done it before, with Dr. Manhattan). It's entirely possible for the rest of the world to unite against America in this case, rather than sympathize with them. Adrian's squid plan could very easily have backfired.