This analysis ignores the effects of WWII. At the end of WWII, the USA was the only industrial economy in the world, not significantly damaged by the fighting.

This analysis ignores the effects of WWII. At the end of WWII, the USA was the only industrial economy in the world, not significantly damaged by the fighting. If you see, the spike of worker union participation is right after the end of WWII. Basically, for a couple of decades the USA had a monopoly on advanced manufacturing. Then as Europe and Japan caught up, there was more of a push towards efficiency as US companies faced more competition