I have seen the effects of mass unemployment for myself.
For centuries, Liverpool was a major port, and built an extensive dock system to serve all its traffic. Whole sections of the city were built as housing for dockworkers, within reasonable walking distance of the docks. These were not wealthy people, but they made an honest living through hard work.
Then containerisation happened, and ships were unloaded by huge cranes instead of armies of men. New, enormous docks were built to accommodate this new method of working and the larger ships it engendered. The old docks, unable to compete on equal terms, closed - putting thousands upon thousands of dockworkers out of work, all at once.
They couldn't just move to another dock or port - all the other ports were containerising too, and the containerised docks required far fewer men to handle a much larger volume of goods. In happier times, they might have gone to work for the railway instead, but British railways were in the middle of a full-scale retreat from goods traffic. Likewise, mines were closing all over the place.
There was thus no other industry that could take on a large influx of unskilled physical labourers, which is what they were if you discounted their docker experience. And besides, who would they sell their houses to in order to move - if they owned them in the first place, that is. If they didn't, they were still stuck paying rent *and* council tax (which wasn't income-linked) without a steady job to pay for them. The only viable way out was the welfare system.
The result was the Toxteth Riots of circa 1980 - Toxteth being one of the more centrally-placed docker districts. If you look in the right places, you can *still* find burned-out buildings from that event. And, even though I didn't live there, for some reason my parents sent me to school there. Several of the other children in my class regularly came in hand-made uniforms, because their families couldn't afford the official ones.
Containerisation was, of course, an overall benefit to the economy, since it greatly reduced the cost of shipping over long distances. But it was a sudden shift which caused a huge amount of localised human misery.