There's always been tension within capitalist economy nations, explained by the GINI index, the CIA's economic measure of inequality within economies. From a material standpoint, most of the poor have little to complain about, especially compared to the hardship the pioneers went through. But there's increasing levels of dissatisfaction, manifested by the rise of Sanders/Trump/AOC, a plummeting birthrate, increases in mental health issues, suicide rate, opioids, etc. It tracks with widening inequalities.
Human beings are social creatures, subconsciously deriving their self-worth from comparing/ranking themselves to others in society. It's not some Democratic plot, it's not AOC preying on lazy Millennials. It's just human nature. People in poor nations often feel more connected to each other, their happiness is measurably higher, even though their material plight is tougher.
When a lot of people in the US see overt evidence of immense inequality, they sense injustice, feel like failures, etc. Their kids sense it, too. The GINI index predicts the distrust Americans experience.
Epidemiologist Richard Wilkinson has been able to accurately predict rates of preventable diseases - diabetes, heart disease, some cancers - *between* US states, based on data on economic inequality. The same measures the CIA uses to assess social stability in other nations.
(I'm not pushing socialism or soaking the rich. I'm just explaining an economic epidemiological perspective.)