Python has actually had concurrency since about 2019: https://docs.python.org/3/library/asyncio.html. Having used it a few times, it seems fairly sane, but tbf my experience with concurrency in other languages is fairly limited.
Iraq peak US troops: range from 168,000 - 192,000 (2007)
Vietnam peak US troops: 543,000 (1969)
Korea peak US troops: 320,000, unclear what year
edit: obviously, Russia's involvement in Ukraine over the last few days would be by far the biggest operation in Europe since WW2. Just not globally (by a long shot).
The sim2real approach can work pretty well as long as you are very in tune with where your simulator falls short relative to the real world and take steps to circumvent those shortcomings.
We were able to train the robot to climb stairs completely by feel/proprioception without any sort of vision. We trained it in simulation, and then transferred it to the real world without issue.