This appeared in Bloomberg Opinion.

The withdrawal of U.S. troops from Afghanistan signals the end of a war that involved close to 800,000 American service members. Defending against new threats will require the U.S. to replenish its all-volunteer force with fresh recruits — a task made harder by the dwindling number of Americans willing and able to serve.

The U.S. currently has 1.3 million active-duty service members. The military needs to find more than 150,000 new recruits every year. In 2020, all the services hit their annual recruitment goals – but those figures were distorted by a historically weak job market, as active-duty service members delayed plans to re-enter the civilian sector. 

At least 70 percent of Americans between 17 and 24 are ineligible for military service due to obesity, mental-health issues, past drug use, criminal records or lack of a high school degree. The Defense Department estimates that just 2 percent of 20.6 million 17- to 21-year-olds have the desired combination of strong academic credentials, adequate physical fitness and an interest in serving.

This limited supply compromises national security. In recent years, the Army has only just barely met the Pentagon’s minimum cognitive-aptitude benchmark for new personnel. Recruits tend to come from a small number of mostly southern states and families of veterans, a group whose share of the population is lower than at any time since World War II. This skewing of the recruiting pool risks widening the divide between service members and the citizens they’re sworn to defend.

The U.S. needs a broader cross section of Americans in military service. More generous enlistment bonuses for candidates qualified for critical positions and willing to sign up for six years; outreach to community-college and technical-college students, who are more likely to have specialized skills and score higher on aptitude tests; more recruiters in communities with low participation; more advertising on social media would all help.

Opening the force to those with histories of truancy or drug use would repeat a mistake made by the Army at th height of the Iraq War. Addressing childhood obesity, substance abuse and poor academic achievement requires greater investment in the country’s K-12 education and public-health systems. The effort is critical — not just for the preservation of American power but also for the strength of America’s democracy.