A few things are driving this.
- The entrance of South East Asia, then China, then India into the global division of labour and the global market for consumer goods and services. This pushed up returns for the wealthy who could hirer cheaper and sell more widely and pushed down returns to labour as workers had to compete with their ever poorer neighbours (although many goods were cheaper and inflation lower).
- A decline in innovation, a la Tyler Cowen. We became much better at doing things from the 1920s-1970s. Most of the modern world was created then and we haven’t created anything like a big a breakthrough as kidney dialysis, chemotherapy, the airplane, TV, refrigerators, air-conditioning, etc., in the last 30 years. The internet is nice, but not a huge boon to GDP.
- Some combination of declining returns in the real economy and rent-seeking in the financial sector has caused a shift from real production to finance. With attendant crises and diminished growth. As it became harder to profit from real production capital fled to finance. As finance became more dominant it became more difficult to profit from real production, a vicious cycle.
- The above graph looks at US incomes and so overstates the divergence. Policy may be set in the main at the national level but production occurs globally. Many people worse off than those living in the US have become significantly better off. The deceleration from the 1980s in the west is mirrored by an acceleration in the rest of the world. Little comfort to some, great comfort to others.
- Policy in the west erred in two ways:
- It sought to trade equality for more growth. Taxes were reduced on the wealthy to incentivise them to innovate more. Unfortunately the incentive effects of tax cuts on the wealthy are weak, especially compared to how much more difficult it became to innovate (see 2) or produce profitable non-financial firms (see 3).
- Secondly, the decline of trade unionism didn’t just make workers more “flexible”. It also caused a decline in worker “voice” in the workplace. Compensating for this, and I would argue provoked by this, there was an increase in occupational licensing (from baby-sitter to lawyers) and centralised directives to protect workers. Where workers could have once demanded whatever protection was deemed necessary with union backing, they now had a significantly weaker on site negotiating position. Workplaces became more intimidating for workers, and more regulated for employers.
UPDATE: Read Noahpinion (do it, it is excellent) for an expansion and deepening of the argument I make in point 1.