It's long been my opinion that you simply cannot destroy the west without mutually assured destruction, so nukes are out. You can't invade and subsequently operate because Americans will never acquiesce to foreign rule, and we are individually armed.
The only way to undo the US/west is to have it undo itself. Seed dissent and promote divisions and hatred among its people. Maybe I was shielded from this as a kid, but it seems these divisions are hatred are sharply on the rise as of late, and it's not outside the realm of possibility this is due to foreign influence via social networks.