America is a decadent country
Transgenderism in children (rejection of reproduction, suicide), tolerance to absurdity, fat acceptance, the list goes on and on.
When an organism is saturated in energy, it begins to invent challenges for itself. You can see this in the purposeful consumption of disgusting food, for reasons of creating the appearance of sophistication. Video games and other such entertainment abound.
To grow, an organism needs challenge. When they are saturated in energy, and work very little to bring energy into their own system, they develop disorders. Their easy life leads to self-hatred and a desire for challenge (hence, zombie-apocalypse fantasizing which is everywhere in society).
Decadence is a natural evolution when power and money are too abundant. Without nuclear weapons, America would be conquered long ago. We persist in our decadence, in the same way an obese man lays in his own shit.
Population will eventually decrease, or invaders will be imported, which will outbreed and conquer us from within.
There is no stopping this. Such a thing would be akin to creating a self-perpetuating machine. If the constituents of a thing have entropy, then that thing has entropy. To deny the fall of a civilization is common, especially for members of that civilization, but all around us are direct signs of the decline. Many are saying economic growth will now never exceed 4%. At some point it will be 0%, and then it will begin to decline.
As it declines, the population will decline - people do not have children in times of economic decline (nor, it should be noted, in times of extreme economic prosperity). Structures of humans will thus compete harder and harder for humans, as structures rely on new humans for their "energy". They will import humans, or they will engage in warfare to obtain humans. Both will destroy the nation.