with a country's economy. The global desire for that export will drive up demand for the country's currency — in Russia's case, the ruble, and in Venezuela's case, the bolívar. That demand drives up the value of the currency, which makes all exports from that country more expensive. So the overreliance on a single export — oil in these instances, but it could be anything — depresses all the other industries in the country.

Now, even as their overreliance on oil wreaked havoc on other industries in their economies, Russia and Venezuela were still pulling in a lot of money from that one export. So they could just import everything else they needed from abroad.

The problem is, this solution only worked as long as oil prices stayed high. Andin 2014, the price of oil on the global market collapsed by two-thirds.

The immediate effect in Russia wasn't hard to predict: The government's deficit ballooned.

Normally, Russia's central bank would have responded by buying up the country's debt to prevent a bigger deficit from driving up interest rates or necessitating spending cuts. The trouble was, this would have put upward pressure on inflation and Russia was already dealing with an inflation problem due to its overreliance on oil.

This was a very foreseeable problem. When the rest of the world is driving up demand for your currency by buying just one of your exports, and then the price of that export plummets, the value of your currency will plummet along with it. And that also puts upward pressure on inflation.