Computer technology. It has eliminated many a job, made others out-dated. There has been a complete change in which disciplines are now in demand. A Bachelor's Degree is now equivalent to a high school diploma. Post graduate work is now required and then only in certain technical fields. A Doctorate in Liberal Arts will get you an entry level job at Wendy's......if there is an opening.
Automation has certainly reduced the labor force, it's incredible what they can make a PLC do to machines now. My last employer invested aprox. 5 million in automated machines in order to cut 7 production positions. At the rate a production worker earned it take years to recover that cost, even if the machine worked as advertised which it did not. It was a maintenance nightmare, one guy dedicated to only those machines, untold hours of downtime and a new area just for spare parts. The worst part, they were Italian built, so no American got any money for them, the installation or part supply (other than me when I assisted the install).
Recently visited a large cereal maker. Very few actual people there, just a ton of conveyors and packagers and few blue shirt maintenance guys waiting for a part to fail. I bet management has no idea where those boxes come from. Automation is a huge part of food processing now because it reduces the chance of contamination greatly, the less hands that touch it the better. Metal detection, x-ray, leak test, better than someone kindna looking at the package as it's packed. Lucky for me a machine will always need maintenance, be it preventative or repair.