James Traub asserts a common assumption:

An ally is not a country that shares your values, but a country that shares your interests. The two categories overlap plenty, of course, because values play a powerful role in shaping a country’s interests abroad.

The first part of this formulation makes sense, but I don’t think the second part is true in most cases. Since the end of the Cold War, most U.S. allies have maintained or created formally democratic governments, and many have adopted neoliberal fiscal and trade policies to one degree or another, but it seems more likely that allied states cultivate the political and economic values favored by the U.S. because they believe it is in their interest to align themselves closely with the U.S. To the extent that the U.S. makes acceptance of these values a condition for a closer relationship, allied states have an incentive to shape their values in a manner consistent with their perceived interests. As long as allies can enjoy a close relationship with the U.S. without pursuing political and economic reforms, and in those cases where allied cooperation is more important to the U.S. than the ally’s embrace of the right “values,” there need not be much overlap at all.

Then again, there are many rising democracies around the world that probably share more values with the U.S. than they share interests. The more democratic and responsive to their own nations that these governments become, the more likely it is that we will see just how divergent their national interests and ours really are. After all, it’s not as if Germany’s interest in increased economic ties with Russia is driven by Germany’s political values, and India’s dealings with Iran and Burma are hardly shaped by India’s democratic values, and those interests tend to put these allied states at odds with the U.S. on many issues. For that matter, improving U.S.-Vietnamese ties have nothing to do with a change in Vietnamese political values and everything to do with shared opposition to Chinese ambitions in the South China Sea.