After WW II, US manufacturing managers assumed they were the greatest and became smugly complacent. Because the Japanese and European manufacturing plants were destroyed during WW II, the US firms initially had little competition and US firms could sell all they could produce, The US made no attempt to innovate new approaches to manufacturing. In addition, US firms padded the number of levels of management to justify higher salaries for the top managers and build bigger empires of flunkies reporting to each manager. They granted organized labor wages settlements out of line with productivity advances. Until recently most US business innovations were in the area of finance with the automation of asset markets, corporate mergers, and junk bond finance.
While the US manufacturing firms went to sleep, the Japanese built new plants with an innovative approach to manufacturing. These innovations in manufacturing should be considered as important as the 19th century US innovations in assembly line manufacturing and replaceable parts.