ROFLOL!! You apparently think you know everything.....
Good luck with that.
That was simply through the application of mechanization, automation, computerization, robotics and improved work methods.
That doesn't happen to be that astounding, but the US government has had just about the same number of working bureaucrats since 1960.
That has happened as a consequence of some really serious computerization.
Recently we changed our battle posture substantially through development and application of what we call DRONES. They are little more than computerized aircraft ~ and speaking of automating unusual things, much of the plowing and seed drilling in the Midwest ~ one of Earth's premiere agricultural regions ~ is now done by automated systems.
Happened right under your nose I am sure.
What do you think happened to the pilots who used to fly the planes to do the same job the drones do? And farmers ~ who's driving the tractor.
We used to have secretaries where I worked. When I retired we'd gotten rid of secretaries ~ there were no more secretaries and every employee could type.
Unless you intend to die early you should be able to see most jobs just disappear. You already saw well over 10% of existing jobs disappear permanently.