“You were a mercenary? Did you kill anyone?” I get this question a lot.

“I really can’t say,” I answer, and it’s the truth. A lot of what I did was secret, or, as we say in the industry, a “zero-footprint operation.”

Mercenaries are back. No one knows how many billions of dollars slosh around this illicit market. All we know is that business is booming because when you need something absolutely, positively done in war, you call the private sector. Missions once conducted by special operations forces or the CIA are now outsourced—I know because I did them.

Mercenaries are deadlier than most people realize, a grave oversight. Last year, a group of Delta Force, Army Rangers, Green Berets, and Marines—America’s most elite troops—were pinned down in Syria. Attacking them were 500 mercenaries, probably hired by Russia. They were not the cartoonish rabble depicted by Hollywood or TV pundits. This was the Wagner Group, a high-end mercenary outfit with artillery, armored personnel carriers, and tanks.

The American commandos radioed for help. Warplanes arrived in waves, including Reaper drones, Apache helicopters, F-22 fighter jets, F-15 strike fighters, B-52 bombers, and AC-130 gunships. Scores of airstrikes pummeled the mercenaries, but they did not waver.

Four hours later, the mercenaries finally retreated. No Americans were killed, and the U.S. military touted this as a big win. But it wasn’t. It took America’s best troops and advanced aircraft four hours to push back 500 mercenaries. What happens when they have to face 1000? 5000? More? Even an undefeated military can lose.

Mercenaries are the second oldest profession, and their return is no surprise. Since 2015, mercenaries have flourished in Yemen, Nigeria, Ukraine, Syria, and Iraq. There are even cyber-mercenaries called “hack back” companies.

And while many might think that most developed nations are averse to using mercenaries, that thinking would be wildly out of touch with the reality of war today. In fact, some Americans think we should outsource 100 percent of our wars. A retired general says we should replace troops in Syria with contractors. So does Erik Prince, the founder of Blackwater and brother of Education Secretary Betsy DeVos. He claims a few thousand mercenaries can win Afghanistan. Crazy as this sounds, the plan has supporters. "Why can't we pay mercenaries to do the work for us?" demanded President Trump of the National Security Council.

“ When conflict becomes commodified, military strategies blend with business ones: think Clausewitz meets Adam Smith. ”

But here’s the problem: privatizing war distorts warfare in shocking ways, and the world is not ready for it. To start, when conflict becomes commodified, military strategies blend with business ones: think Clausewitz meets Adam Smith. For-profit warriors are not bound by political considerations or patriotism; in fact, this is one of their chief selling points. Instead, they are market actors, and their main constraint is not the laws of war but the rules of economics. And when money can buy firepower, it’s the super-rich who will become a new kind of superpower—thus making war increasingly more unconventional because it’ll enable wars without states.

To think we can regulate the market for force is naïve. International law is impotent because mercenaries can kill law enforcement. Also, who will go into Syria and arrest all those guns for hire? Not the UN or Marines. Others think we should legally go after their clients, but don’t count on it. Consumers are foreign governments, off-shore companies, and the mega-rich—all difficult to sue.

As Machiavelli warns, mercenaries breed war and suffering. So where does that leave us—and what does the future of war look like—in a world where mercenarism is inevitable? First, recognize the new rules of war—especially the change to warfare that comes with the return of for-hire soldiers. We need to use market mechanisms to shape the market for force: incentivize good behavior, drive out the bad, and develop innovative strategies that undermine private warfare. And we must raise our strategic IQ. Mercenaries are multiplying because they sell more than firepower—they offer plausible deniability in an information age. This makes them attractive to anyone who wants to wage war without consequences, and that’s everyone.

Denial is not a winning strategy. War has moved on, and we must move with it if we want to win.