It's pretty well documented in primary sources that just about every manufacturer has moved their factories in pursuit of lower labour costs. Jurisdictions with

It's pretty well documented in primary sources that just about every manufacturer has moved their factories in pursuit of lower labour costs. Jurisdictions without labour protection regulation tend to unsurprisingly have lower costs for unskilled and semi-skilled labour. This isn't just about unions, but (very costly) safety regulations too. This was all a fully predicted outcome of international free trade. US-based manufacturers simply can't compete with unregulated labour pools of people willing to work capably in toxic and dangerous conditions for most of their waking lives just to survive. It's the same reason we have to import enormous amounts of agricultural labour. Depending on your political leanings you may take this as a cry to deregulate labour, or to increase tariffs. The status quo however dooms most domestic manufacturing to be noncompetitive.