I apologize for jumping on your post so harshly.
No problem. Your posts usually have some thought behind them so I try to extend the benefit of the doubt. Besides, I get overextended from time to time. Back in '77....
Structural change is something I have been rattling around in my head lately. I think we agree mostly but there are some significant differences in our assessments so they are worth exploring.
I assume you meant 1930. Yes and no on those two historical times as structural changes. As I believe you would agree one can not get a sudden collapse without something being inherently wrong within the structure. I think we have the same understanding whatever the semantics used.
Structural unemployment is a concept a lot like secular stagnation; it can be valid in looking at growth and long term trends, but it can't just double in a few months. Structural unemployment does not explain recessions or depressions and neither does secular stagnation. In the same way business cycle theory cannot explain persistent
unemployment (which structural unemployment does) or slowing long term economic growth (which secular stagnation does).
Your agreement is our disagreement.

I do not believe that aggregate demand can be raised sufficiently. The reason why is because there has been structural change, there is always structural change, and previous business models are not working. The divergence is getting further and further all the time. This leads to the second suggestion, labor mobility. There are no jobs in rural America or the inner cities but one can not go chasing jobs from there to somewhere else. One of my favorite, maybe
the favorite, phrases is, "Cast Down Your Bucket Where You Are." Whatever the new economy is, and no one knows, it will have to grow from where people are. I do agree wholeheartedly with training and education but think about child care. In inner cities and rural America child care might be much less of a problem due to the greater chance of extended family at hand.
My point is that with inadequate demand, there is no policy for structural unemployment that works well. If an economy does not grow, then all job training does is rearrange who the unemployed are.
The issues of child care and transportation are questions of access. When the jobs exist, people must still be able to access them. Some of this the market will automatically do. In the 60's I observed buses in Chicago paid for by employers going into poor neighborhoods to transport workers to factories in the suburbs. Land was cheaper there (if the factories had remained near the poor neighborhoods workers would have walked or used public transportation, but you don't walk from the Stockyards to West Chicago and public transportation didn't run between the two areas and low income factory workers in Chicago didn't own cars) and it was more profitable to move the workers than move the factory. The better solution would have been public transportation between the areas, but employers couldn't wait for the politics to be worked out. End of labor shortage.
In this sense I am more in line with with the Progressive Caucus or Black Caucus' budgets than with the President's budget. Ryan's budget is not only Draconian it is the fast way to ruin that could possibly be conceived. The Ryan budget is the deer in the headlights, frozen with fear. The President's budget addresses the problem with the right attitude but if one really reads the conclusions which are found in the research we need to put pretty much every last dime we can beg, borrow, or steal into our future and the dividends will be multiples on the dollar.
From your lips to voters ears.