President Trump’s decision to scrap the Iran nuclear deal, established under President Obama, has major implications across the globe and for the White House. Just the FAQs

Our leaders seem interested in toppling Iran’s theocracy. But do they want a new U.S. military draft? Because make no mistake, that’s what it will take.

(Photo: Vahid Salemi, AP)

With U.S. withdrawal from the Iran nuclear deal, the installation of John Bolton as national security adviser, new sanctions and demands on Iran and a White House that appears committed to doing the heavy lifting for our friends and allies, regime change in Iran may well be back on the menu.

Should a serious public relations campaign for regime change begin, we will assuredly hear some familiar songs: the mullahs’ theocracy is weak and will swiftly collapse; our “man in Tehran” will be embraced by the people; the war will practically pay for itself; and most important, we won’t need to put any American “boots on the ground.”

All of these claims should be treated with enormous skepticism, but the last one is the most dubious.

Any serious effort to end the Iranian theocracy will not only require American troops, but will also almost certainly break our vaunted All-Volunteer Force If you like the idea of regime change in Iran, you had better love the idea of a new American draft.

We have seen for decades that American air power alone is insufficient to topple a government, whether it be Hitler’s Germany, Ho Chi Minh’s Vietnam or Saddam’s Iraq. (Bolton’s predecessor, Lt. Gen. H. R. McMaster, dubbed this idea “the vampire fallacy”). Our Sunni Arab allies are stalemated in Yemen and distinctly averse to sending troops to Syria. The idea that they would invade or occupy Iran is risible. The Washington regime change crowd’s preferred Iranian proxy is a hated cult called Mujahideen-e Khalq.

But if the mullahs are to be overthrown, it will be by American soldiers and Marines. Even if the Islamic Republic were to somehow collapse on its own, concerns about radiological material, the security of the Strait of Hormuz or another massive wave of refugees would probably drive the U.S.to intervene with ground troops.

U.S. politicians and generals sometimes like to point out that the volunteer military has successfully endured a decade and a half of sustained combat and a ceaseless cycle of deployments. This is not the whole story.

Despite the enormous amount of money expended there, Iraq was by historical measures a low-intensity war. Total combat deaths for American forces over eight years were about the size of a brigade, and losses in Afghanistan roughly half that.

Yet a modest increase in force structure required the military to greatly lower its standards, doubling felony waivers for Army recruits from 2003 to 2006, for instance.

A massive increase in the use of civilian contractors (more than 50 times the ratio in Vietnam) also hid the volunteer system’s cracks. The All-Volunteer Force was barely able to sustain two large, but low-casualty, campaigns — neither of which has resulted in anything resembling a U.S. strategic victory.

Occupying Iran would be a challenge of an entirely different magnitude than Iraq or Afghanistan. The Islamic Republic has a population of 80 million people — more than double that of either of its war-torn neighbors. However, it shares the ethnic diversity of those neighbors: only 61% of Iranians are Persian. This has caused some hawks to salivate, but it should instead provide another strong warning about the second- and third-order effects of regime change in Iran. As in Iraq and Afghanistan, removing Iran’s government could unleash the furies of sectarianism and communal strife. The odds are exceedingly low that U.S. troops will be “greeted as liberators.”

Iran’s geography is equally daunting. At 636,000 square miles, it is effectively the size of Western Europe. Ringed by mountains, ocean, and swamp, Iran is a fortress. Most of its population lives in the mountains; the lowland salt flats and deserts are largely uninhabitable. American forces, dependent on motorized and aerial movement and supply, are particularly ill equipped to handle Iran’s military geography.

The force with which we would occupy Iran is also not as resilient as most Americans probably think. Even now, in a time when most troops are not seeing direct combat, the the volunteer force is struggling just to maintain numbers and standards. The Air Force, Marine Corps, and Navy are each short of a full quarter of their required fighter pilots. The Army recently announced that it is already 12,000 recruits behind on its recruiting goal for 2018 and will not make mission.

The Pentagon stated last year that 71% of Americans between the ages of 17 and 24 are ineligible to serve in the U.S. military, most for reasons of health, physical fitness, education, or criminality. The propensity of this age group to serve is even lower. The likely demands and casualties of a war in Iran would spell the end of the All-Volunteer Force, requiring the conscription of Americans for the first time since 1973.

There is ample evidence that American foreign policy elites haven’t learned much from Iraq or Afghanistan; one need only look at the latest headlines from Libya or Syria. But perhaps even our modern Bourbons in Washington can grasp one simple lesson from the post-9/11 campaigns: Wars have an uncanny tendency to take on a life of their own.

Regime change in Iran would bring a host of consequences, many of them unknowable, but almost all of them negative for America and the region. There is one outcome we can be sure of, however: Occupying Iran would be the death of America’s all-volunteer military and necessitate a return to a draft.

Gil Barndollar served as a Marine infantry officer from 2009 to 2016 in Afghanistan, the Republic of Georgia, Guantanamo Bay and Bahrain. He holds a Ph.D. in history from the University of Cambridge.