It's the same as what caused it in the 1930's. Decades earlier a flood of grossly overpopulating cultures (then mostly more Catholic Irish, and Poles, and Italians - along with more Germans, and Balkan and Baltic people, and Jews from eastern Europe) undercut wages. Their even bigger flood of children killed the labor market and dropped wages to rock bottom. Just before, in the 1920's we squandered away our capital base in a frenzy of spending as if the party would never end.
We repeated all that -- but with different cultures flooding in -- through the past couple decades and we have ended in the same disastrous spot. This time cheap container shipping also took away most heavy industries, and others, to the worst overpopulating cultures with desperate, dirt cheap labor and good ports.
Like their classic Marxist mentors then, today's neo-Marxists blame the "greedy capitalists" who did exploit the situation. Marxists have always distracted us from the real causes trying to throw all the blame on their enemies.
