Yeah, median income in the UK is about at the level of Mississippi, as is much of Western Europe (Western, not Eastern!). The US is just ridiculously wealthy, and our income inequality is largely a matter of the absurd heights reached at the top, with wide distributions. OTOH, wealth disparity (or even just the perception of wealth disparity) can be politically destabilizing and lead to some pathological social issues. Greater relative social mobility and greater (perceived?) wealth equality seems to result in a better sense of fairness, a sense of fairness is key to social cohesion and trust, and social trust is key to producing wealth. Though, social trust is necessary but hardly sufficient. Likewise, perceived mobility and equality seems necessary but not sufficient for healthy political and civic culture.