[strken]

The one I was thinking of was slavery in the US, and the technological innovation in the south vs the north.

A better example might be the low price of labour-intensive hand-picked fruit (particularly berries) in the US and the correspondingly low agricultural automation. It's not that machines don't exist, or that berry picking is going to prevent the next Facebook, it's that they aren't cost effective in the short to mid term even when longer term investment would eventually improve the whole industry. This is really hard to measure and I don't have any good sources for either side of the argument right now.

I also want to make a distinction between skilled and unskilled migration. I don't think skilled migration is harmful to the social fabric in an enduring way, nor migration with the same proportion of skilled and unskilled labour as the host country.