At least there's some economics work now going on to try to understand the sources & cause of inequalities' increase over the last 30 years.
However, it still doesn't appear that they've identified it (them). In the following piece Dean Baker rips apart an OECD analysis of cause while substituting some other variables which he shows accounts for a substantial part of the cause: The financial sector. This is another of the half-assed economic efforts since Baker spends no time explaining or even guessing which policy or condition changes in particular provided the financial sector with the ability to create / increase inequality increasingly over time since the late 70's.
In my own analysis (see my past posts on median family income relative to GDP changes) I find that the indicator of inequality (rate of median family income change relative to GDP change over time) is due to the rapid and sustained increases in productivity without a corresponding increase in wages & salaries at the median family income level. In fact, individual white males at the median even lost income over standard of that time frame, so that the very slight increase observed was due to 2nd income earners (wives) entering the workforce in greater numbers --- basically just to maintain a median standard of living.
That increased productivity without the labor force sharing in the proceeds at the median income level had to manifest somewhere in the distribution of incomes --- and it did, increasingly improving incomes relative to GDP for the income brackets higher up on the income distribution curves. This suggested that the productivity gains were made at the lower levels of production labor skill levels... where the greatest number of labor were (are)employed. The question that needs to be addressed is why the labor effort displaced by increased productivity wasn't able to share in the proceeds of the increases in productivity and GDP rate of change that followed the rate of change of productivity .... persistently and increasingly over the last 3 decades... and continuing.
I can see how the financial sector participated ... i.e. by financing the productivity improvement methods employed by producers of goods and services, but I cannot see how this participation would have increased the financial sector's share of national income since the same was true of the financial sector prior to the late 1970's when median family income increased in lock step with the growth rate of GDP. Somehow and for some reason not yet clearly demonstrated, the upper income brackets were able to extract an increasing share of income from the median family labor force as productivity improvements occurred.
My own assumption based on empirical data is that the labor force was unable to maintain their share of GDP growth as productivity improved because they increasingly lost bargaining power ---- both because of labor union's loss of clout, and because as more labor is displaced it increases the available unused labor supply in that sector, hence by elementary supply/demand relationships, keeping a lid on wages/salaries growth.... effectively suppressing it even as GDP continued to grow. The net effect was full to maintain full employment, but at lower relative wages/salaries at the median and lower income labor levels.
International trade plays a significant role in the reduction of labor bargaining power, since domestic goods production which is shown to be non-competitively priced relative to that which can be purchased at lower costs from non-domestic supplies and sources forces either improved productivity (lower labor costs) domestically, or reductions in production due to being displaced by imported goods at lower prices. In real effect as long as there is free flow of capital domestic labor is forced to compete with non-domestic labor sources. With increasing imports at lower costs than can be produced domestically with higher labor wages/salaries, the economy still hums along and continues to grow, albeit at lower growth rates, even though domestic labor is being paid less relative to GDP growth rates. Sooner or later though the loss of purchasing power at the median income level reduces domestic consumption, and hence further reductions in GDP growth... which not unsurprisingly means that capital investment in domestic enterprises is replaced by capital investment in area's with greater growth rates or where roi is greater.
I frankly don't see a simple way out of the situation that increases inequality of incomes other than by gov't redistribution thereof. There's certainly no free-market incentive for capital investment to increase domestic wages to keep pace with GDP growth when there's more than ample domestic labor available at lower wages/salaries, and when not, then more than ample labor available offshore somewhere.... and in fact with increasingly lower and lower costs of increasing productivity, even more incentive for capital investment to support greater productivity growth rates... exacerbating the already increasing supply of domestic labor, hence reducing it's wage / salary earning power at a greater rate, forcing even greater inequalities of incomes.
The bottom line is that as long as there's a free-flow of capital without a corresponding free flow of labor, then capital will continue to flow to the lowest labor markets to obtain the greatest roi, reducing wage/salary growth in area's which are substantially greater in standard of living... stagnating or even reducing it. If GDP growth rates are maintained, then the rate of salary / wages growth will continue to fall further behind the GDP growth rates, the extracted value add thereby being distributed upwards, increasing inequality growth.