It turns out that war in the 21st century is not just about killing bad guys. In Iraq, Gen. David Petraeus has demonstrated that to win modern battles soldiers must do more than attack enemies — they also must make friends. It is our local allies who have been able to distinguish — in a way no computer, drone, or satellite can — between loyal Iraqis on the one hand, and al-Qaeda terrorists and Iranian agents on the other.

In addition to warfare, there is lawfare: the rules and regulations that govern the fighting. Last week, after much controversy and delay, the House finally passed a bill to restore to our spy agencies the authority they need if they are to have any chance of keeping tabs on terrorists abroad. The bad news: Last week, the Supreme Court, in a 5 to 4 decision, granted to unlawful combatants at Guantanamo the right to challenge their detention in federal court. Honorable POWs have never enjoyed such constitutional protections.

There also is what might be called jawfare: the war of ideas, the war against the supremacist ideologies that drive terrorism, and for freedom and other Western values. James K. Glassman, sworn in this month as Under Secretary of State for Public Diplomacy and Public Affairs — thereby putting him in charge of this command — candidly acknowledges that “since the rise of Islamic terror we haven’t done enough on this front.”

What have I left out? The economy, stupid. Economic battles are a pivotal — yet little understood — component of war. For example, you probably know that the Battle of Stalingrad was a turning point in World War II. What you might not have learned in History 101: It wasn’t just that the city was an industrial hub that bore the name of the Soviet dictator. More important, as author Robert Zubrin has noted, it was the gateway to the great oil fields of central Asia. “Unless we get the Baku oil,” Hitler told a general he assigned to Stalingrad, “the war is lost.”

In this same period, the Japanese coveted what is now Indonesia not for its rubber and coconuts but for its petroleum. The U.S. responded to Japanese aggression in Southeast Asia by declaring an oil embargo against Japan. Pearl Harbor followed.

Thirty-two years later, the Arab members of the Organization of Petroleum Exporting Countries (OPEC) launched another oil embargo, this one to punish the United States and other nations that supported Israel after the Jewish state was attacked by Egypt in the Yom Kippur War.

The price of oil quadrupled causing serious economic dislocations. Then-President Nixon responded with price controls which led to maddeningly long lines at gas stations. In March 1974, the embargo was lifted, but the effects of the “oil shock” would be felt for years to come.

Now, 34 years later, we are suffering through a second oil shock, again caused by OPEC — the cartel’s goals are to keep petroleum prices high and increase the power of its members — as well as by rising global demand. Oil prices have doubled in the past year and quadrupled in the past six. As energy researcher Gal Luft has pointed out, the consequence is a historic transfer of wealth “to the coffers of a small group of oil-producing nations, most of them authoritarian and unfriendly to the West.”

In recent congressional testimony, Luft noted, too, that should oil reach $200 a barrel, OPEC could “potentially buy the Bank of America in one month’s worth of production, Apple Computer in a week and General Motors in just three days.” A 20-percent share of every S&P 500 company could be theirs in just 18 months.

Foreign ownership is not necessarily bad. But acquisition by private investors is one thing; ownership by “sovereign wealth funds” controlled by despots hostile to America is quite another. We would not allow the U.S. government to buy Citicorp or Fox News. By what possible reasoning should we be more welcoming of Islamist regimes — in many cases the same regimes that deployed what they called the “oil weapon” against us just three decades ago?

If we understand that we are fighting a war, we also should understand this: There is no precedent for winning a war while lavishly funding one’s enemies.

And speaking of those enemies, imagine a Gulf sheik sympathetic to Osama bin Laden’s goals but uncomfortable with his methods. He might say to the terrorist master: “Why blow up buildings we can purchase — with the infidels themselves providing the money in return for a few drops of the oil that Allah, in His infinite wisdom, has placed beneath our desert sands for just this purpose?”

— Clifford D. May, a former New York Times foreign correspondent, is president of the Foundation for Defense of Democracies, a policy institute focusing on terrorism.