So, what does $8,500 buy you? The figure is a measure of an entire country's GDP adjusted for differences in prices around the globe and divided by its population. It's not a median income, nor is it for an entire household; a typical household in one of these countries might have something like $15,000 in total purchasing power every year. (As a guide, the United States has per capita GDP of about $48,000 and median household income of about $53,000, but households in the United States average about 2.5 people, versus more than 3.5 in Brazil.) That's by no means a high-income family, but in most countries it represents middle-class, or at least working-class, respectability. Such a household might spend $1,500 a year on taxes, $400 a month on housing, $50 a week on food, and $120 a week on everything else.
The latest South American country to reach the $8,500 threshold was Colombia, in 2011. If it follows the same path as the other four, the election in 2014 will replace the center-right government of Juan Manuel Santos -- and previously Álvaro Uribe -- with a center-left government. A center-left government isn't always easy to spot in South America; plenty of observers thought Brazil's Luiz Inácio Lula da Silva might turn out to be a loose cannon or fellow traveler of Venezuela's Hugo Chávez, but he was nothing of the sort.
In fact, Santos, who was elected in 2010, may himself qualify for the center-left distinction someday. He is already moderating some of Uribe's harsher policies, and his coalition in Colombia's congress commands support from left-wing liberals. In other words, the transition may already be happening.
Of course, not every country with more than $8,500 per capita in purchasing power has attained the magical combination of political and economic stability, even in South America. Though the World Bank's figures don't go back before the 1980s, it looks like Argentina crossed the $8,500 line sometime in the 1960s, coinciding with the progressive government of Arturo Illia. But Illia was elected by a flawed process and soon ousted in a military coup. Venezuela may have reached $8,500 even earlier and has had elected governments since the late 1950s. Yet as in Argentina, its living standards were essentially stagnant until the past decade or so.
The difference here may be as simple as one word: globalization. Brazil, Chile, Peru, and Uruguay have been able to bolster their growth with foreign investment to a degree that Argentina and Venezuela never could, not just in the extent of the investment but also in its diversity. Globalization has also made South American countries less isolated, both politically and culturally. It's easier than ever for their people to compare the performance of their governments with others around the world.
With that in mind, could countries in other regions follow the South American example? Possibly, but the similar and shared histories in South America make the case for the $8,500 rule particularly compelling. And their story of development is by no means the only one; in East Asia, the narrative of state-organized industrial growth in Japan, South Korea, and Taiwan is equally notable. More likely, up-and-coming regions like South Asia and Sub-Saharan Africa will write their own stories of stability and success.