Ever since Bolivia and Chile kicked off the post-colonial era in South America by going to war, nations on the American continent have had problems getting along.

Nationalism remains almost as strong today, although the intervening years have seen plenty of attempts at regional cooperation. Dreams of political union may have melted away, but efforts to build economic alliances continue. From the Southern Cone Common Market (Mercosul) to the North American Free Trade Agreement (Nafta), several agreements have been signed, although all remain controversial.

But globalization has added a new kid on the block: China. Central and South American nations that once looked north to the regional powerhouse of the United States, or east across...