Dani Rodrik has a short, clear post on (a) why countries are tempted to engage in protectionism during recessions and (b) why they shouldn’t. It only uses 1st-semester macroeconomics. The bottom line is that the preferred outcome is for all countries to engage in fiscal stimulus at the same time. The hitch is that most of the developing world can’t afford to. The implication is that it is in the interests of the wealthy countries to find a way to support the developing world.