On Saturday night — right at midnight — the United States’ agreement with the Afghan Taliban is scheduled to take effect. While the agreement says the United States will withdraw its troops from Afghanistan, we know nothing of what it says about military contractors. But contractors have provided the lion’s share of U.S. military staffing in Afghanistan, and other post-9/11 wars.

Here’s what you need to know about military contractors in Afghanistan and Iraq.

The contractor force is largely hidden.

Since the U.S. government began keeping track in the mid-aughts, contractors have made up more than half of the military personnel working for the United States in Afghanistan and Iraq.

But stories about contractors rarely make the news. In a 2010 study, Lee Sigelman and I tracked news coverage of contractors and service members between 2003 and 2007. Articles mentioning service members ranged from 476 to 1,251 each quarter. Those mentioning contractors ranged from one to 95 a quarter — a dramatically smaller number. As Steven Schooner, T. Christian Miller and others have documented, even their deaths remain unsung, making them a “disposable army.” According to The Washington Post’s Afghanistan Papers, more than 3,814 U.S. contractors have died in that war — while only 2,300 U.S. military personnel have. The deaths of contractors overtook those of soldiers in 2010. That imbalance significantly reduces the political costs of U.S. wars.

Further, this shadow army’s invisibility gives politicians a chance to change strategies without the media or the public noticing. How many people know that in the first three years of the Trump presidency, the use of private security contractors in Afghanistan increased by more than 65 percent — after declining under President Barack Obama?

To be sure, politicians can use contractor deaths as a reason to act if they want to. That’s what the Trump administration did at the beginning of January, when it issued the White House memo to Congress justifying the decision to kill Iranian Gen. Qasem Soleimani with a drone strike. The stated reasoning: The strike was payback for an Iranian rocket attack that killed a single U.S. contractor.

But despite periodic reports and series on contractors by ProPublica and others, the mainstream U.S. media does not regularly pay attention to contractors. As a result, they’re subject to political manipulation. These dynamics have contributed to what journalist Dexter Filkins has called “The Forever War.”

Which means that U.S. contractors could help sustain hostilities in Afghanistan, even after the U.S. pulls out its troops.

Most contractors are not U.S. citizens.

Despite the image of ex-military Americans like those working for Blackwater during the Nisour Square shooting, the Pentagon hires a vast majority of contractors from within the country or from other countries. The U.S. Defense Department calls the latter “Third County Nationals,” or TCNs. A Congressional Research Service analysis of military personnel in Iraq and Afghanistan in 2008 showed more than 40 percent were TCNs, while almost 40 percent were local Afghani or Iraqi forces and only 20 percent were U.S. citizens.

In a recent book, political scientist Adam Moore offers many examples of how the relationship between U.S. decision-makers and TCNs can have serious unintended consequences, sometimes far from the conflict itself. Moore opens his book, for instance, by describing an event in 2004 in which the Iraqi rebel group Ansar al-Sunna kidnapped and killed 12 Nepalese contractors working in Iraq, and placed execution videos online. Thousands of enraged Nepalese took to the streets, attacking their Muslim neighbors.

As demand for TCNs has grown, so too have employment firms, or “body shops,” that recruit labor. These body shops sometimes mistreat personnel, confiscating and holding their passports, skimming off their wages, and committing other abuses associated with human trafficking. U.S. government overseers — and even prime contractors — are often unaware of these practices. Indeed, Moore argues that prime contractors treat TCNs better while subcontractors are prone to abuse. Human trafficking aside, the price for labor varies in different parts of the world — which has resulted in a racial hierarchy, whereby pay for the same work varies based on each contracted employee’s race or nationality. As the workers realize this, they get angry and sometimes jump to other companies, protest or strike.

This “invisible army,” as investigative journalist Sarah Stillman called it in the New Yorker, includes people with many different backgrounds, experiences and loyalties. That brings both benefits and risks. They could be spies. They could have mixed loyalties. They could funnel money to the enemy — as happened when Afghan private security contractors ran a “protection racket” in which U.S. payment for security services went to militias, some with direct ties to the Taliban.

Companies contracting with the United States often take short cuts, relying on nationality as a proxy for loyalty to — or antagonism toward — U.S. causes. But that’s a bad choice. When Chelsea Manning leaked classified documents to WikiLeaks, for instance, the firm KBR banned TCNs from using telecommunications — even though Manning was (and is) an American citizen. A system that many contractors describe as unfair exacerbates risks to the United States, as people may lose their commitment to the work or even work against the United States.

Contracting can undermine U.S. security, at great cost.

Finally, while using contractors may save costs on particular contracts, the system of contracting ends up being quite costly because it allows for misbehavior. The system has allowed networks of corruption that have milked the U.S. budget and funneled money in ways that have undermined U.S. security goals, as has been documented repeatedly — in Defense Department inspector general reports for Iraq and Afghanistan, the Watson Institute’s project on the Costs of War, and elsewhere.

In the past 10 years, the U.S. government has made some progress in ensuring that contracting enhances rather than undermines security. The 2020 National Defense Authorization Act (in sections 887 through 889) aims to further that progress, requiring improved oversight and integrating best practices and standards more thoroughly into U.S. policy. But these steps are just the beginning.

If the United States signs a deal as expected, watch for what it says — or does not say — about contractors. Will they stay and help the Afghan government? If so, on whose dime and with what rules and oversight? Contractors are likely to be as important as troops for Afghanistan’s future.

Deborah Avant (@DeborahAvant1) is the Sié Chéou-Kang Chair for International Security and Diplomacy at the Josef Korbel School of International Studies, University of Denver, and the author, most recently, of “Civil Action and the Dynamics of Violence”(Oxford University Press, 2019).