I have a word of advice for American allies outraged by alleged NSA spying on their leaders: Grow up. That means you, Germany. You too, France. And you, Brazil. Mexico, too. Also the EU and the UN.

Does the National Security Agency spy on your leaders? Probably. Do you spy on leaders of allied states including the United States? Probably. You just don’t have the resources or capability to spy as effectively as the NSA does. But if you did, you would.

Don’t bother denying it. All states subscribe to the principle enunciated by Lord Palmerston, the 19th century British foreign minister and prime minister: “We have no eternal allies, and we have no perpetual enemies. Our interests are eternal and perpetual, and those interests it is our duty to follow.”

In the pursuit of their interests, all states need as much information as possible about the actions and (even harder to fathom) the intentions of other states, even (or perhaps especially) those with whom they are allied at the moment.

There is pretty much no state on whose automatic loyalty you can count. Witness how our close allies the French refused to support the Iraq war but took the lead in Mali. Or how the Germans chose to sit out Iraq but participated in Afghanistan. And that’s only looking at security policy; economic policy is also a big deal.

Of course the leaders of France, Germany, Brazil, et al. know this. But their voters don’t.

The reason why all advanced nations spend a lot of money on intelligence is, in part, to help them answer such questions.

Sure, a much bigger part of the intelligence budget goes, as it should, to analyzing the actions and intentions of enemies, but even if you are narrowly focused on bad actors such as Iran or al Qaeda, you must have accurate information on the actions of your allies: Will the Germans support tougher sanctions? Will the Italians cooperate in a rendition? And so on. That’s why nations spy on each other in private, even while pledging eternal friendship in public.

That’s why the US intelligence community fears penetration by the intelligence service of Israel (an ally) at least as much as it fears penetration by the intelligence services of avowed enemies such as Iran and Cuba. And with good cause.

There is a partial exception: the “five eyes” alliance between the United States, Britain, Canada, Aus­tralia and New Zealand. Those nations, which have been sharing sensitive signals intelligence since World War II, probably don’t spy on each other’s leaders — but they do spy on each other’s citizens. In fact this intelligence sharing allows them to do an end-run around prohibitions on domestic surveillance: The Brits can spy on our citizens, we can spy on theirs and then we can share the results.

Everyone else — every other country outside the “five eyes” — is fair game for American spying, and we are fair game for theirs.

Of course the leaders of France, Germany, Brazil, et al. know this. But their voters don’t. Much of their anger is faked for public consumption. The only outrage is that anyone is outraged.

Max Boot is a senior fellow at the Council on Foreign Relations. From the group blog Contentions at commentarymagazine.com.