In the winter issue of International Economy magazine, Adam Posen - newly returned from Bank of England to run the Peterson Institute for International Economics - offers this account of wage stagnation in the US and other developed countries:
[T]he size of the world labor force doubled at the low-skill, low-wage end by bringing China, Eastern Europe, and parts of India into the global economy. This put huge downward pressure on some wages. …
The second cause is there basically was a corrupt capture of a big chunk of our political and economic system where a lot of legislation, regulation, and corporate decisions were directed to maximizing the benefits for the few people in charge of financial firms at that particular time.