Like Twelve said, nationalism plus many parts of the country having criminally underfunded education, therefore a feeling of misplaced inferiority with coastal big cities. Bad actors then helping in manifesting this anger in mismanagement of government to say all government is bad, to keep people from asking the important questions about larger corporations screwing you and Republican hypocrisy about fiscal responsibility(though this applies also to the ignorance that Democratic voters can have when it comes to wage stagnation not being caused by poorer populations and immigrants, so we can flip the chessboard in how the Democratic establishment can maintain a base yet also meekly loses to Republicans despite the country mainly being liberal when we get human society's changes at this juncture). Bad actors help in maintaining ignorance and misplaced distrust in technology or higher learning as only the elites oppressing you, and label the elites as liberals.
Thus why the cycle of us going back to absolutely moronic/corrupt conservative presidents continues l, even when by all rights it shouldn't happen. So nationalism nurtured by ignorance with people not knowing how to handle or do anything about the truth.
We aren't the greatest country on Earth, we are good at taking from others and using people, plus nuclear stockpile proliferation(while making the hypocritical argument to de-nuclearize everyone else with the excuse of deterrence).
That and the "you got oil? We give you democracy" heavy handed BS. So yeah, the shining beacon on the hill mentality is real gross when you take an honest look at history. The real reason for no big war breaking out right now is that while profiteering over skirmishes through the military industrial complex is good, even people in the establishment understand how demoralizing war is for the populace, even taking nationalism as the catalyst.
The mechanism works just enough the gears don't break, but then you have the Reagans Bushs, Trumps, who corrode the rust of the gears, so its bound to break eventually(though on the other side, the Dems telling people they have hope and then giving it up at the first opportunity to lose to the GOP to maintain "unity" also strains things, not to mention their own vying for political power and wanting to keep it, but refusing to fight when they can depresses their voters and so is part of why this cycle continues).