From Ezra Klein we have the following:
Those at the 34th percentile of income in the United States are at the 90th percentile globally, and those at the 50th percentile in the United States are at the 93rd percentile globally. Even the very poorest Americans — those at the 2nd percentile of income in the United States — are at the 62nd percentile globally.
So a person who represents the poorest 2% in the US has more income than 62% of the worlds population – and don’t forget this excludes the implicit security net you gain by being in a developed economy (and excludes the fact that wealth disparities may be more significant at a global level). And the following graph:
Now I would note that the fact that there is global inequality does not imply that domestic inequality is “fair” – or that policy is appropriate. But it does imply that there are other more important sources of income inequality in the world.
Another thing, the key issue isn’t inequality of income – it is inequality of opportunity. The fact that people in the developed world restrict the movement of labour, and do not help improve institutions in poor countries, is doing more to reduce equality of opportunity than anything.
In NZ, I came from a poor family in a country town – thanks to the way the country is structured I have been able to borrow, invest in my human capital, and work my way up to be an economist and live comfortably. That sort of mobility on the basis of effort is what we want in society. And this is the thing that people born in poor countries do not have access to, which is why the real injustice is being perpetrated on these people.