Actually about 5 million people in the US have been identified last year by the United Nations Human Rights Council as living in "3rd world conditions" or absolute poverty (defined as "conditions characterized by severe deprivation of basic human needs, including food, safe drinking water, sanitation facilities, health, shelter, education and information) with almost 60 million living below the poverty line. You don't need recent civil conflict and mud huts to have third world conditions.
Remember that the US is a massive country and sadly despite it's immense wealth and power, plenty of people live in almost Dickensian levels of poverty for various reasons both institutional or otherwise.
https://undocs.org/A/HRC/38/33/ADD.1
I agree that having such standards define the US post 1945 is really hard barring nuclear war or some sort of civil war wrecking everything, but millions of people in the United States have it really, really rough you can't ignore that. You have the ultra rich and you have the ultra poor.