Over the past couple of years, I have strongly resisted the trend toward teaching international trade early in an introductory micro economics course, where it appears in many introductory textbooks. Those who want to teach it early, point out that understanding division of labour and comparative advantage lie at the heart of understanding any exchange.
I don't deny this.
The problem is that so many of the incorrect oppositions to free trade involve the misuse of macro economics, as is so aptly pointed out by the author of the textbook I use in his comment about a posting by Scott Sumner.
Scott then goes on to propose an explanation of these events that can be viewed as consistent with the textbook Keynesian model. In particular, I interpret Scott as saying that the retreat from free trade reduced business confidence, shifted the investment function I(r) to the left, and thereby reduced aggregate demand.
One general lesson from his discussion is that it is often hard to distinguish shocks to aggregate supply and shocks to aggregate demand. Policies and events that adversely affect aggregate supply (e.g., trade restrictions) will often reduce the marginal productivity of capital, decrease investment spending for given interest rates, and depress aggregate demand as well. In the short run, the indirect demand-side effects of "supply shocks" could potentially be larger than the direct supply-side effects.
Maybe the pure theories of international trade are also pure micro, but dealing with the criticisms of the basic theories requires an understanding of macro as well.