NYTimes.com:

Trump seems to imagine an American autarky: a closed nation, self-sufficient and indifferent to the rest of the world.

…

Imposing tariffs, expanding territory, a new Mexican war and a traditional vision of the American people — these are what the nation needs, Trump says, to be “great again.” In which case, MAGA cannot possibly refer to anything in the 20th century, when the United States essentially built the modern international order, as much as it must refer to some time in the 19th century, when the United States was a more closed and insular society: a second-rate nation whose economy was many magnitudes smaller and less prosperous than our own.