Economic crisis, mounting national debt, excessive foreign commitments -- this is no way to run an empire. America needs serious strategic counseling. And fast. It has never been Rome, and to adopt its strategies no -- its ruthless expansion of empire, domination of foreign peoples, and bone-crushing brand of total war -- would only hasten America's decline. Better instead to look to the empire's eastern incarnation: Byzantium, which outlasted its Roman predecessor by eight centuries. It is the lessons of Byzantine grand strategy that America must rediscover today.

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Fortunately, the Byzantines are far easier to learn from than the Romans, who left virtually no written legacy of their strategy and tactics, just textual fragments and one bookish compilation by Vegetius, who knew little about statecraft or war. The Byzantines, however, wrote it all down -- their techniques of persuasion, intelligence gathering, strategic thinking, tactical doctrines, and operational methods. All of this is laid out clearly in a series of surviving Byzantine military manuals and a major guidebook on statecraft.

I've spent the past two decades poring over these texts to compile a study of Byzantine grand strategy. The United States would do well to heed the following seven lessons if it wishes to remain a great power:

I. Avoid war by every possible means, in all possible circumstances, but always act as if war might start at any time. Train intensively and be ready for battle at all times -- but do not be eager to fight. The highest purpose of combat readiness is to reduce the probability of having to fight.

II. Gather intelligence on the enemy and his mentality, and monitor his actions continuously. Efforts to do so by all possible means might not be very productive, but they are seldom wasted.

III. Campaign vigorously, both offensively and defensively, but avoid battles, especially large-scale battles, except in very favorable circumstances. Don't think like the Romans, who viewed persuasion as just an adjunct to force. Instead, employ force in the smallest possible doses to help persuade the persuadable and harm those not yet amenable to persuasion.

IV. Replace the battle of attrition and occupation of countries with maneuver warfare -- lightning strikes and offensive raids to disrupt enemies, followed by rapid withdrawals. The object is not to destroy your enemies, because they can become tomorrow's allies. A multiplicity of enemies can be less of a threat than just one, so long as they can be persuaded to attack one another.

V. Strive to end wars successfully by recruiting allies to change the balance of power. Diplomacy is even more important during war than peace. Reject, as the Byzantines did, the foolish aphorism that when the guns speak, diplomats fall silent. The most useful allies are those nearest to the enemy, for they know how best to fight his forces.

VI. Subversion is the cheapest path to victory. So cheap, in fact, as compared with the costs and risks of battle, that it must always be attempted, even with the most seemingly irreconcilable enemies. Remember: Even religious fanatics can be bribed, as the Byzantines were some of the first to discover, because zealots can be quite creative in inventing religious justifications for betraying their own cause ("since the ultimate victory of Islam is inevitable anyway …").

VII. When diplomacy and subversion are not enough and fighting is unavoidable, use methods and tactics that exploit enemy weaknesses, avoid consuming combat forces, and patiently whittle down the enemy's strength. This might require much time. But there is no urgency because as soon as one enemy is no more, another will surely take his place. All is constantly changing as rulers and nations rise and fall. Only the empire is eternal -- if, that is, it does not exhaust itself.

Back when I was a senator, my colleague Russell Long had a favorite retort for someone speechifying against him in the Finance Committee. "Well, your lips say, 'No, no, no,'" Russell would say, "but your eyes say, 'Yes, yes, yes!'" I've thought a lot about Russell and the perils of miscommunication recently as I've tried to untangle a mystery that has bothered me -- and tainted U.S. relations with Russia -- for nearly two decades: Just how exactly did the United States end up expanding NATO into Eastern Europe after the Cold War, when NATO's ostensible purpose would seem to have expired along with the Soviet Union itself?

The Russians insist that NATO expansion violated an explicit promise made by the first Bush administration; the Americans have not only denied it, but seem quite unaware of how much this dispute has haunted U.S. dealings with Russia. During a trip to Moscow, Mikhail Gorbachev, the last Soviet leader, told me that during his 1990 negotiations with U.S. Secretary of State James Baker about Germany's reunification and the removal of 300,000 Soviet troops from East Germany, the Russians made it clear that they didn't want German reunification within NATO. The negotiations went back and forth with little progress. Finally, according to Gorbachev, Baker looked at him directly and said, "Look, if you remove your troops and allow unification of Germany in NATO, NATO will not expand one inch to the east."

When I spoke with Baker, he agreed that he told Gorbachev that if the Soviet Union allowed German reunification and membership in NATO, the West would not expand NATO "one inch to the east." But "the east," for Baker, meant East Germany -- not Eastern Europe. The United States later dialed back Baker's offer even further, saying that legally, if Germany reunified, the White House couldn't promise no NATO expansion into East Germany. The final compromise was that no "non-German" NATO troops could be in East Germany, but German troops were allowed. According to the American participants in the negotiation, NATO expansion east of Germany didn't even come up.

Then, of course, President Bill Clinton expanded NATO to the Czech Republic, Hungary, and Poland, and President George W. Bush pushed it even further in early 2004. Russia perceived these actions as threatening, and they remain a bone of contention today. As former Russian presidential candidate Grigory Yavlinsky once told me, "We Russians might not understand financial puts and calls, but we do understand tanks."

Baker and Gorbachev are honorable men, and I was confused at first by how their stories differed. But thinking of Russell's old line, I saw the possibility for honest miscommunication. Given President George H.W. Bush's earlier vow at the 1989 Malta summit that if Gorbachev allowed Eastern Europe to go its own way, the United States wouldn't take advantage, one can see how Gorbachev might have thought Baker was referring to any eastward expansion, not just expansion into East Germany. And, indeed, when I asked former U.S. national security advisor Brent Scowcroft what had happened, he said that Gorbachev "had misinterpreted" Baker's words. The misunderstanding, which has caused so much enmity and mistrust, tells us one thing for sure: In diplomacy, always make sure your eyes are saying exactly what your lips do.

To some, Barack Obama might seem like a modern-day JFK, FDR, or Lincoln. But when it comes to foreign policy, his roots go a little further back: to Prince Klemens von Metternich, foreign minister of the Austrian Empire from 1809 to 1848 and the patron saint of multilateralism. Sure, Obama is a liberal democrat while Metternich's autocratic tendencies helped spark the revolution of 1848. But Obama's cosmopolitan approach to diplomacy and his constant invocation of "common interests" when dealing with governments from Caracas to Moscow to Tehran are vintage Metternich. This diplomatic impulse—derived in both cases from a personal taste for legalistic moderation—is admirable, but problematic, and Metternich's own successes and failures reveal why.

The prince's greatest triumph was the Concert of Europe, a loose alliance of the leading powers at the time: Austria, Britain, Prussia, and Russia (and later France). An earlier incarnation of today's U.N. Security Council, the group held brief congresses whenever a crisis threatened the continent's stability. Throughout, Metternich's influence loomed large. He rejected unabashed power politics, endorsed the idea of an international community with collective solutions, and persuaded liberal states such as Britain to cooperate with their autocratic counterparts.

Like his 19th-century predecessor, Obama has had early success in building coalitions, as at the London G-20 summit in April when he encouraged a modern-day Concert to pledge $1.1 trillion toward stabilizing the economic crisis and helping out poorer countries. But sooner or later Metternichian diplomacy disappoints its practitioners—not with what it does, but what it doesn't do. It's relatively easy to coordinate actions between countries that already want the same thing, as with the 1803-1815 Napoleonic Wars, when Metternich ultimately cemented an anti-French alliance based on a shared fear of Napoleon. When common goals don't exist, however, Metternich-style diplomacy can't create them. Take 1866, when Prussia—unconvinced that it shared the same goals as the rest of Europe—defeated Austria for leadership of the Germanic states. Austria left the ranks of great powers, a victim of its own belief in the tenacity of shared interests.

Today, Obama faces challenges that are no less worrisome. Consider what might happen if the world economy heals quickly. Some countries may decide they no longer need to play nice, and shared interests like the ones that propelled the G-20 negotiations will evaporate. Another problem is subtler but more insidious: Those who follow in the Austrian statesman's footsteps can inherit a bias for stability and miss out on opportunities for dynamic change. Such myopia prevented an earlier Metternichian, Henry Kissinger, from envisioning the Soviet Union's collapse. Unless Obama comes up with a foreign policy that goes beyond the Austrian prince's rigid multilateralism, he too might not end up seeing the world clearly.