Most Americans likely think that our trade policies have been largely the same since the Republic's earliest days. The assumptions are that we're free traders now and always have been; also, that we've long been a manufacturing power, boosting exports. If we sometimes lose in global competition, the main cause is that other countries don't play fair.

The truth is more complicated, as economist Douglas Irwin of Dartmouth College shows in his monumental study of U.S. trade policy since the Revolution, "Clashing over Commerce." Just published, it is an essential companion to the debate over U.S. President Donald Trump's trade agenda.

Irwin quickly dispels the notion that manufacturing has traditionally characterized U.S. exports. To the contrary, the United States initially resembled what would today be called a "developing country." He writes: