Manufacturers traded manufacturng capability for importing finished (or near-finished) products as a way to increase their profits. They are now addicted and the detox procedure will be lengthy and painful.... as people with 401K investments will also find out.
It happened because of 75 years of industrial growth, American inventors, American tycoons and bankers taking risks, millions of immigrant laborers and farmers to feed them, conflict and violence, several Panics and one Great Depression. After the second war we rebuilt Europe, continued arming our military and fostered the rebirth of Western Eurpoean industry as an ally in the Cold War. All the while we made money and built more factories but prifit is the god of capitalism and cheaper labor means greater profit. Unions had raised wages at the same time as allowing workers to buy the products they made,buy that house in Levittown, send their kids to college. International competotors arose, first Japan then Western Europe. It was competition . We beat Japan but others arose. Now we assemble, we don’t make and tge infrastructure needed to return will take longer to build than Pres Trump has left in office.