I should point out that the slave owners were the ones that were primarily in favor of free trade. Their agrarian economy forced them to import most of their goods, and the north generally was protectionist. But that opens up a states' right debate that I don't want to deal with now.
All of which has nothing to do with the current discussion...
So what changed between 1940 and 1960 that suddenly ushered in the free trade era? Why did we go from the world's biggest exporter to the world's biggest importer?
Exactly. But getting rid of it was the right thing to do. Same with tariffs. I believe they'd be for lowering or eliminating those today as well. You say they wouldn't be. Who knows?
Why did we go from the world's biggest exporter to the world's biggest importer?
Who cares?!? Do you realize what our economy and average income has done throughout the increase in our trade imbalance (which paleos have been screaming about for years)?