So American companies outsourced their manufacturing to low-wage countries, like China, Vietnam (and South Georgia?), who would do the dirty work for next to nothing.
Then, the goods would be imported into the USA for those companies, who would proceed to make dirty big profits off the backs of what is almost slave labourers.
And now Trump (and I'll omit the adjectives I have in mind) slams tariffs of close on 50% on those countries. He is shooting himself in the foot to such an extent that he hasn't got a leg left to stand on.
If Trump wants manufacturing to go back to the USA, fine. But it'll be a darn sight more expensive than having it done in the sweatshops of Hanoi and Beijing.