There’s likely some truth to these narratives [of automation etc]. But a new report from the Organization for Economic Cooperation and Development (OECD) offers a more straightforward — and political — explanation: American policymakers have chosen to design an economic system that leaves workers desperate and disempowered, for the sake of directing a higher share of economic growth to bosses and shareholders.
The OECD doesn’t make this argument explicitly. But its report lays waste to the idea that the plight of the American worker can be chalked up to impersonal economic forces, instead of concrete political decisions. If the former were the case, then American laborers wouldn’t be getting a drastically worse deal than their peers in other developed nations. But we are.
And here's the graph which shows it:
[Apparently this is from the 2018 World Inequality Report]
As for what USAians can do about it, very little. Their political system is unique among western democracies in suppressing competition, effectively instituting a two-party oligarchy. There is no peaceful, democratic way to fix it. Which means that the only option for Americans who want a fairer deal is to move to a better country.
(As for New Zealand, as The Spinoff points out, things aren't exactly rosy here - though this is looking at wealth inequality, which is even more extreme than income inequality).