As U.S. President-elect Donald Trump contemplates tariffs and other limits on trade, he might consider the results of such protectionist measures in two economies on the other end of the hemisphere, in Argentina and Brazil.

For decades, South America’s two largest economies have tried to shield their workers from global trade, largely through high tariffs and regulations that promote domestic production over imports. The World Bank ranks Argentina and Brazil among the world’s most closed big economies.

In...