Nations are sometimes destroyed by military force. But more often, nations are brought down by the destruction of their core sense of identity and shared community.
Once you know what makes a country great, it becomes much easier to destroy it. So that’s the way to go if you want to destroy a once great nation, and leave it a mere shell of its former self.
If somebody really hated the United States, or else worked for its geopolitical enemies, the most efficient way they could bring it down would be to destroy it from within. If you can take away from America the things that make it truly great, what is left will no longer matter.
So the first thing you should do is convince the American people that its greatest virtues are actually vices. Diversity, equality, inclusiveness — the very defining American traits that Lincoln pointed proudly to at Gettysburg — need to be perceived as weaknesses, rather than the strengths they truly are.
Once you manage to plant that sickness into the soul of the American people, it will grow like a cancer. Millions of Americans will forget who they are, and will change from being a free and generous people to becoming suspicious, selfish and filled with hate.
But who could have so much hatred for America that they would try to destroy it in such a monstrous way?