The problem is that most of “us” - first world, USA, Europe, Japan, ANZ, etc. - are the 20% with the extra money. The billion in China or India or Africa are primarily in the 80% that have the remaining 5% of wealth.
One common wisdom is that the French Revolution was a revolt of second sons, the ones with nothing to lose under primogeniture. The system broke down over the demand to tax the nobility same as the merchant class. The bottom 50% were just cannon fodder for the street demonstrations. At a certain point, a giant crowd coming from buildings can swarm a bunch of muzzle-loaders faster than they can re-load.
Bernie Sanders, for example, managed to seduce a huge proportion of the Democratic primary voters; enough to persuade Hillary to alter course on a number of policies. Speaking as a Canadian with a good income who pays about 28% in total income tax, and enjoys full medical care with no co-pays, no deductibles - I cannot understand why the USA puts up with the medical mess it currently has.
The bigger danger is when hefty big countries - Egypt, India, Pakistan, Indonesia, China, Nigeria - have the clout to challenge the 21% and demand a better share of the world’s resources. We are already beginning to see the fallout of this - the massive number of non-Syrian economic migrants trying to make it into Europe. Turkey already extorted a degree of cooperation in return for stemming the Syrian tide; however, it is only the beginning. (Law of unintended consequences - get rid of strong man Ghaddafi and Libya is a wild west for migrants…)
The problem is, the “hired help” - CEO’s and lawyers and executives - used to be paid decently more than the grunts. Nowadays, it’s changed; the CEO’s have stratospheric salaries, transforming themselves into the 1%; the grunts continue to get the short end of the shaft, lower wages, no pension, ludicrous health benefits, etc. This wealth is ot flowing to the third world - it’s accumulating in the top.
Trump so far defied the expectation to get elected by pushing all the right buttons with the lower 50%. It’s only a matter of time before some Bernie Sanders type figures out the same message - portray the rich as greedy pigs hoarding everything that belongs to the “hard working American patriots”… If that person can avoid sounding like a socialist - i.e. push the right buttons - he will get elected and transform the world’s (second) biggest economy.
But China is no better. nothing motivates a population better than envy. The Chinese government has managed to stay afloat by continually increasing the economic status of the population, while friends of the oligarchs get richer and richer. Any significant downturn in the next while could see than country implode, or explode to distract the population.
The major revolutions of the last centuries - English, French, Russian, Iranian, Soviet - all happened when the rising economy took a downturn and the peoples’ expectations were not being met.
May you live in interesting times.