[RcouF1uZ4gsC]

Saying the price of labor in the 1950s was high due to unions is a simplistic explanation. Prior to that, almost every industrialized nation had been turned into rubble( see WWII) except the United States. In addition, labor participation especially for the high paying jobs was severely limited due to sex ( high proportion of single income households with with stay at home moms) and race discrimination.

So you have a high demand for labor coupled with a lower supply and thus increased wages. Labor was a contributor to it, but not the main driver. As other countries became industrialized and more people that had previously not been in the workforce entered, the supply and demand for labor in the United States changed and the industries that were heavily unionized got destroyed by the competition (see the auto industry)

[kesselvon]

Foreign trade was not a big component of the US economy until well after. Are unions the sole reason for high wages? No. But being able to negotiate as a collective instead of individually does drive wages up.