I'm not an economist, so these are speculative, but seem reasonable based on the fact that we're talking about loss of wealth from households below median:
Loss of life (specifically heads of household) due to the wars (I'm guessing most military households, being young and having maximum education of high school to "some college" will be below median)
Increased energy costs (gas being a marginal cost would hit people with less marginal income harder).
Loss of jobs to automation (I'm thinking secretaries, anything that can be replaced by an iphone, etc)
Declining birth rate (last I heard total high school graduations were supposed to peawould tend to lead to oversaturated teaching jobs, also relatively low-paying.
Chrysler was in distress long before the recession.
