Matthew Shaffer lives in Cambridge, Massachusetts.

When President Cristina Fernández de Kirchner initiated the nationalization and expropriation of the Argentine assets of YPF, an oil company owned mostly by Spanish interests, it came as no surprise to anyone who has visited the country recently or watched it closely. The theft, a consistent manifestation of the Kirchner personality and the mercurial character of the Argentine political class, was more a return to business as usual for the country than a shock — and goes a long way toward explaining why Argentina is poor.

In January 1912, an impartial observer of Argentina and the United States would have had trouble guessing which had a more promising future. Both enjoyed the low-hanging fruit of abundant, underpopulated land. The Argentine pampas were as fecund, tillable, and flat as the American Midwest. Argentina had a long coastline ideal for exporting the agricultural products that were grown inland. Immigrants from all over the world were rushing in. Argentina had one major advantage over the States: It had never relied so heavily on slavery for agriculture. So it had never experienced such a wrenching civil war, nor was it destined for the racial strife and inequality that would be the major blot on America’s future. By 1912, Argentina had even started to enjoy some soft power: The tango — which had originated in Buenos Aires’ slums — had just hit Paris and would soon be the rage in New York and Finland. The capital was marketing itself as a fully European city transplanted directly into the Americas.

In January 2012, I caught a flight to Buenos Aires with a cheap Air Canada ticket, a psychological desperation for more sunlight than Boston would enjoy until April, and a vague curiosity about why Argentina, which had once so resembled the United States, was now so different. What had happened in the intervening 100 years?...

If you want a one-word answer to the question “Why isn’t Argentina rich?” your best bet is coups. Between 1930 (when, only a year after Black Thursday, Argentina’s future may have looked even brighter than America’s) and 1976, Argentina endured at least six. Until 1930, its per capita GDP had closely tracked that of countries like New Zealand, Australia, and Canada. But constant political instability in the decades that followed threw Argentina off track. The reasons are basic: When a country is unstable, it is risky to make the long-term investments required for growth. When dictators and oligarchs use the economy to reward their friends and punish their enemies, markets can’t guide the structural evolution and modernization of the economy. Political revolutions leave a country economically retrograde. By 2000, Argentina’s per capita GDP was about a quarter of that of Canada, New Zealand, and Australia. It had largely missed the boat of the 20th century’s spectacular growth....