A decade ago, I found myself in a precarious position. I was in Burundi, sipping a Coke with Domitien Ndayizeye, the country’s then-president, U.S. Ambassador Jim Yellin, and several others. We had an emerging catastrophe on our hands.

Ten years earlier, the Rwandan genocide left a trail of ash and tears in its wake, claiming 800,000 lives in 90 days—nearly a soul a minute. Since then, Rwanda had recovered, but neighboring Burundi remained at war with itself, ravaged by infighting with Hutus massacring Tutsis and vice versa. In 2004, the United States had intelligence that Hutu extremists wanted to trigger a new genocide that would end Tutsis once and for all. My job, in collaboration with everyone sipping Cokes in the president’s living room, was to prevent this, without anyone outside the room knowing it was a U.S.-led effort. And succeed we did. The Hutu rebels attacked the capital in November 2004, in an attempt to assassinate the president and spark mass killing. A fierce night battle erupted in the streets of Bujumbura, and the extremists were killed or beaten back into the jungles of the Congo.

What made my presence in that room notable: I was not a member of the CIA. Nor was I covert U.S. military operative or government employee. I came, instead, from the private sector––a contractor to many, a mercenary to some.

Burundi was but one of my numerous assignments. I helped raise a new army in Liberia, bought and shipped weapons from eastern Europe to Africa, and shaped the environment in difficult places. My experience was hardly a unique one, and has actually grown more common in the years since I left Burundi. U.S. Special Operations Forces, for instance, have contractors working in Syria, performing tasks ranging from intelligence analysis to warzone logistics and possibly training foreign fighters, as they once did in Iraq.

Now, as President Obama prepares to hand off combat operations in Iraq, Afghanistan, Syria, and elsewhere, to his successor, he’s also bequeathing a way of war that relies on large numbers of guns-for-hire while, at least formally, restricting the number of American “troops” sent overseas. Since 2009, the ratio of contractors to troops in war zones has increased from 1 to 1 to about 3 to 1.

Private military contractors perform tasks once thought to be inherently governmental, such as raising foreign armies, conducting intelligence analysis and trigger-pulling. During the Iraq and Afghanistan wars, they constituted about 15 percent of all contractors. But don’t let the numbers fool you. Their failures have an outsized impact on U.S. strategy. When a squad of Blackwater contractors killed 17 civilians at a Bagdad traffic circle in 2007, it provoked a firestorm in Iraq and at home, marking one of the nadirs of that war.

Contractors also encourage mission creep, because contractors don't count as "boots on the ground." Congress does not consider them to be troops, and therefore contractors do not count again troop-level caps in places like Iraq. The U.S. government does not track contractor numbers in war zones. As a result, the government can put more people on the ground than it reports to the American people, encouraging mission creep and rendering contractors virtually invisible.

For decades now, the centrality of contracting in American warfare—both on the battlefield and in support of those on the battlefield—has been growing. During World War II, about 10 percent of America’s armed forces were contracted. During the wars in Iraq and Afghanistan, that proportion leapt to 50 percent. This big number signals a disturbing trend: the United States has developed a dependency on the private sector to wage war, a strategic vulnerability. Today, America can no longer go to war without the private sector.

No international laws exist to regulate the mercenary industry.

Why did this happen? During the wars in Iraq and Afghanistan, policymakers assumed a quick and easy victory. As former Defense Secretary Donald Rumsfeld said in 2002, the Iraq War would take “five days or five weeks or five months, but it certainly isn't going to last any longer than that.” When these wars did not end in mere months, the all-volunteer force found it could not recruit enough volunteers to sustain two long wars. That left policymakers with three terrible options. First, withdraw and concede the fight to the terrorists (unthinkable). Second, institute a Vietnam-like draft to fill the ranks (political suicide). Third, bring in contractors to fill the ranks. Not surprisingly, both the Bush and Obama administrations opted for contractors.

Today, 75 percent of U.S. forces in Afghanistan are contracted. Only about 10 percent of these contractors are armed, but this matters not. The greater point is that America is waging a war largely via contractors, and U.S. combat forces would be impotent without them. If this trend continues, we might see 80 or 90 percent of the force contracted in future wars.

Contracting is big business, too. In the 2014 fiscal year, the Pentagon obligated $285 billion to federal contracts—more money than all other government agencies received, combined. That’s equal to 8 percent of federal spending, and three and a half times Britain’s entire defense budget. About 45 percent of those contracts were for services, including private military contractors.

This means that contractors are making the ultimate sacrifice. Today, more contractors are killed in combat than soldiers—a stunning turnaround from the start of the wars Iraq and Afghanistan, when fewer than 10 percent of casualties were contractors. By 2010, more contractors were dying than troops. However, the real number of contractor deaths —versus the “official” tally—remains unknown.

The United States has developed a dependency on the private sector to wage war, a strategic vulnerability. Today, America can no longer go to war without the private sector.

Even more troubling: Most of those fighting for the United States abroad aren’t even Americans. Private military companies are multinational corporations that recruit globally. When I worked in the industry, my colleagues came from almost every continent. According to a recent Pentagon report, just over 33 percent of private military contractors in Afghanistan are U.S. citizens.

Many of the larger private military companies also hire local “subs” or sub-contractors, often invisible to U.S. government officials and reporters. In 2010, during the height of the wars, a Senate investigation found evidence that these “subs” were linked to murder, kidnapping, bribery, and anti-Coalition activities. Similarly, in a 2010 report titled “Warlord, Inc.,” the House of Representatives found that the Department of Defense had hired warlords for security services. What happens to these subs when the big contractor goes home? In some notable, alarming cases, they go into business for themselves, breeding mercenary markets in the wake of a U.S. intervention.

For example, a U.S. Senate investigation in 2010 found that the British private military company ArmorGroup sub-contracted two Afghan military companies that it called “Mr. White” and “Mr. Pink” to provide a guard force. The investigation found evidence that they were linked to murder, kidnapping, bribery, and anti-coalition activities.

Giving birth to such markets is just one of the many ways that contractors encourage dangerous policymaking. Unlike the Pentagon or CIA, private military companies do not report to Congress, circumventing democratic accountability of the armed forces. Worse, they shield themselves from inquiry by invoking the need to protect proprietary information and are not subject to Freedom of Information Act requests, unlike the military or intelligence community. This makes them ideal for dangerous missions requiring plausible deniability. Sometimes, even Congress can’t find out what these firms do.

This effectively lowers the barriers of entry into conflict, inviting moral hazard. Take, for example, Obama’s strategy to defeat the Islamic State, essentially a “light footprint” campaign that (theoretically) involves few ground troops. It eschews the Bush administration’s big and costly military presence overseas, and shuns the quagmire of “nation-building.” Instead, in theaters ranging from the Middle East to South Asia, it relies on precision strikes from U.S. aircraft, clandestine ground units, and local allies. However, you cannot hold ground with airplanes, special-forces raids, and unreliable partners. Terrorists will return once U.S. forces leave. This means you can never achieve victory, when your victory conditions are “deter” and “defeat” ISIS.

In response, the Obama administration has quietly accelerated deployments. From an initial 274 troops sent to Iraq in 2014, the White House has crept up to 4,647 troops, the maximum allowed under the current troop cap. But these troops are only half the story. The U.S. government has surged another 4,970 contractors onto the ground. And a footprint of nearly 10,000 doesn’t look so light.

Contractors, then, allow policymakers to wage war outside of the public eye. Their deaths rarely attract headlines the way those of fallen American soldiers do. And yet the consequences are no less far-reaching for being hidden. America’s reliance on contractors to fight its wars has launched a new breed of mercenary around the world. 2015 saw major mercenary activity in Yemen, Nigeria,Ukraine, Syria, and possibly Iraq. Mercenaries in these places are not new; what is new is the increased size and expanded scope of their work. For example, in Nigeria, they pushed out Boko Haram, an Islamic terrorist group, in a few months. The Nigerian military could not achieve this in six years.

No international laws exist to regulate the mercenary industry. What we’re left with: If anyone with enough money can wage war for any reason they want to, then new superpowers will emerge: the ultra-rich and multinational corporations. Oil companies and oligarchs should not have armies.