American foreign policy stands on the brink of substantial belt-tightening. The mounting expenses of servicing the growing national debt, combined with the skyrocketing costs of Social Security and Medicare as the 78-million-strong baby-boom generation retires, will leave less money for American initiatives abroad.

As I argue in my new book The Frugal Superpower: America’s Global Leadership in a Cash-Strapped Era, the burden that these obligations will impose on Americans – in the form of higher taxes and fewer benefits – will weaken public support for the expansive international role that the United States has played since World War II.

This will change the world, and not for the better. American foreign policy, for all its shortcomings, has underpinned political stability around the world. How, then, should the US adapt what it does abroad to minimize the damage to global security caused by its straitened circumstances? Here are three rules for a frugal superpower.

Rule I: No More Nation-building

During the first two post-Cold War presidencies, the US conducted military interventions in Somalia, Haiti, Bosnia, Kosovo, Afghanistan, and Iraq.

The motives for these interventions varied, but all led to American efforts to establish working governments – nation-building – that proved protracted and frustrating.

The relevant institutions cannot be built quickly and cannot be imported, ready-made, from abroad. For this reason, among others, the enterprise has not found favor with the American public.

To its difficulty and unpopularity another drawback to nation-building must now be added: its expense. The US government will no longer be able to afford to invest hundreds of billions of dollars (the cost in Iraq alone will run into the trillions) trying to supply other people with decent government.

Moreover, such projects make a far smaller contribution to US and global security and well-being than do other American foreign policies – policies that the US should make every effort to continue.

Rule II: Concentrate on the Elephants

"Don’t chase the rabbits,” an old saying has it, "because if you chase the rabbits, the elephants will kill you.” Somalia, Haiti, Bosnia, Kosovo, Afghanistan, and even Iraq qualify as rabbits – distractions from what should be the focus of US foreign policy.

The functional equivalents of elephants are Europe, East Asia, and the Middle East. These are three of the most important parts of the world, and in each the American military presence plays a constructive role.

In the first two, the US reassures each of these region’s countries that there will be no sudden change in the balance of power that will threaten them.

In Europe, Germany can be confident that the US would help to contain an aggressive Russia, while Russia knows that Germany will remain tied to, and thus restrained by, the US. In East Asia, American air and naval forces provide a check on China, but also serve one of China’s strategic interests by keeping Japan from conducting an independent military policy.

To keep the peace in both regions, a continuing US military presence of some kind will be needed. Complete American withdrawal could lead to suspicion, arms races, and, in the worst case, wars among the countries of Europe and Asia.

In the Middle East, the US confronts Iran, which seeks to expand its power by any means it can, to oust neighboring countries’ governments in favor of ideologically sympathetic forces, and ultimately to evict America from the region.

Nuclear weapons would make the threat posed by the Iranian regime all the more severe. Indeed, containing Iran while thwarting its nuclear ambitions is the single most urgent priority for today’s cash-strapped American superpower.

Rule III: Raise the Gasoline Tax

Iran’s quest to dominate the Middle East threatens the world because the region accounts for so much of the oil on which the global economy depends. If the world used less oil, Iran would become less threatening, because its radical rulers rely on oil revenues to purchase domestic support and pursue their regional goals.

Reducing oil revenues by using less oil would also weaken other international troublemakers, actual and potential – Hugo Chávez of Venezuela, for example, and Vladimir Putin of Russia. Moreover, some of the money that the world pays for Saudi Arabia’s oil finds its way into the coffers of terrorist organizations.

No single measure would do more to make the world a less dangerous place than a substantial reduction in its consumption of oil. And no single measure would do more to reduce global oil consumption than a sharp increase in the tax on gasoline in the country that consumes more of it than any other: the US.

If Americans had to pay more for gasoline, they would use less of it.  With a high gasoline price, alternative sources of energy such as ethanol and alternative forms of transportation such as electrically powered automobiles would become commercially viable.

None of this would happen immediately. In the short term, Americans would have to make modest economic sacrifices in the form of higher fuel prices. Such sacrifices, however, would be well worthwhile.

They would help to ensure that, even in an era of retrenchment in American foreign policy, the world would continue to enjoy the most important benefits of the expansive foreign policy that the US can no longer afford.

Michael Mandelbaum, Professor of American Foreign Policy at Johns Hopkins University’s School of Advanced International Studies.