When does 32,200 – 60,000 = 109,000? That seemingly inaccurate equation represents the estimated number of Islamist-inspired terrorists when the war on terror began, how many the U.S. has killed since 2015, and the number that fight today. And it begs the question of just how can the terror ranks grow so fast when they’re being depleted so rapidly.

As early as 2003, then-Secretary of Defense Donald Rumsfeld hinted at the potential mathematical problem when he asked, “Are we capturing, killing, or deterring and dissuading more terrorists every day than the madrassas and the radical clerics are recruiting, training and deploying against us?” In his memo, Mr. Rumsfeld correctly identified that both sides have a vote: the U.S. can deplete the terror ranks, while the terror groups and their supporters can replenish them.

What Rumsfeld had not yet imagined, however, was the possibility that military force might inadvertently benefit terror recruitment efforts. Specifically, he ignored the blowback a marauding U.S. military might engender among the Muslim world.

In 2009, General Stanley McChrystal pushed the conversation in that direction. He pointed to the counterintuitive aspects of terror recruiting. Calling it “COIN Mathematics,” he laid out his argument. “Let us say that there are 10 [insurgents] in a certain area. Following a military operation, two are killed. How many insurgents are left? Traditional mathematics would say that eight would be left, but there may only be two, because six of the living eight may have said, ‘This business of insurgency is becoming dangerous so I am going to do something else.’ There are more likely to be as many as 20, because each one you killed has a brother, father, son and friends, who do not necessarily think that they were killed because they were doing something wrong. It does not matter – you killed them. Suddenly, then, there may be 20, making the calculus of military operations very different.” 

Though McChrystal did not explicitly connect U.S. military operations to the perceptions of the broader Muslim community, Osama bin Laden and his number two, Ayman al-Zawahiri, certainly did. Five years before 9/11, bin Laden railed against the presence of the U.S. military in Saudi Arabia, home to the two holiest sites of Islam. On other occasions he spoke of the “American crusader forces” and “American occupiers.” His recurring theme of grievance centered on the U.S. waging war with Islam. Later, in 2005, al-Zawahiri put an exclamation point on it. In a letter to the leader of al Qaeda in Iraq, he reminded him, “The Muslim masses…do not rally except against an outside occupying enemy, especially if the enemy is firstly Jewish, and secondly American.”

Polling indicates that bin Laden and al-Zawahiri’s strategy has significant traction throughout Muslim-majority countries. When asked if “the United States’ interference in the region justifies armed operations against the United States everywhere,” more citizens agreed than disagreed among the 11 nations surveyed. That staggering trend even held true among the populations of supposed allies like Kuwait, Jordan and Iraq. Only in Egypt did more disagree than agree, though 39% still expressed support for attacks on Americans everywhere.

The implication is clear: it is time to stop focusing on killing terrorists. The seventeen-year American military campaign against terrorism, which began in Afghanistan but spread to Pakistan, Iraq, Yemen, Libya, Syria, Somalia, and most recently to Niger, has failed to stem the jihadist tide and has created more problems than it has solved. It has also cost the United States nearly 7,000 lives, more than 52,000 wounded, and an estimated 5 trillion dollars.

The idea that the United States should kill fewer terrorists may strike some as heresy and others as simply foolish. But as General McChrystal said, “I have found that the best answers and approaches may be counterintuitive; i.e. the opposite of what it seems like you ought to do is what ought to be done.” 

So if killing terrorists isn’t working, what will? We do not pretend to have all the answers. But the time-honored military practice of “murder boarding” may help provide inspiration. Despite its ghoulish name, “murder boards” have been successfully used throughout America’s military history. The process, as the name implies, is meant to be merciless. The privilege of military rank gets set aside, as does the pride of those assembled. The goal is to assess – as objectively as possible – through all that has happened to avoid repeating mistakes and to ensure mission success.

Sixteen years in, the President and Congress should finally “murder board” the war on terror and consider new strategies. Until then, counterinsurgency math will continue to frustrate the country’s lacking strategy.