North Korea’s successful test of an intercontinental ballistic missile has brought to the fore the most consequential foreign policy question now facing President Trump: Should the United States go to war to eliminate the threat of North Korea’s nuclear weapons?

So far, the debate in Washington over preventive military action has centered on the nature of the threat. Can a more capable North Korea be deterred from using nuclear weapons against the United States and its allies? Will it engage in nuclear blackmail, sell weapons to terrorists or other rogue regimes, or try to unify the peninsula by force? These are important considerations, but not the only ones that matter. Any decision to attack North Korea must also take into account the extraordinary human, military, and economic costs the United States and its allies would bear for years to come. Odds are good that America would be signing up for a nation building project of epic proportions.

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The immediate human consequences of war on the Korean Peninsula would be stark. Even a limited military intervention could escalate into a larger conflagration. According to the nonpartisan

Congressional Research Service

, hundreds of thousands of civilians could die within days of the conflict. South Korea would face an assured artillery barrage on Seoul, if not a nuclear or chemical attack from North Korea, whose ballistic missiles can also range Tokyo, the world’s largest city, putting millions at risk.

A major humanitarian crisis would unfold in North Korea. Food supplies and basic health care would be scarce, exacerbated by massive refugee flows numbering in the millions. Hundreds of thousands of political prisoners and detainees would also need critical attention. Post-conflict security demands would be similarly daunting. North Korea has the fourth largest military in the world at over a million strong with more than seven million reservists. Even as foreign forces worked to seize nuclear sites and materials, stocks of chemical weapons would be scattered around the country, along with caches of conventional weapons in underground tunnels and facilities. Surviving factions could ignite civil war and insurgency. As a result, stabilization and peacekeeping tasks could require more than 450,000 troops.

Complex governance questions would instantly emerge: What happens to the existing North Korean bureaucracy, the ruling Korean Workers Party, and members of the internal security services? Knotty problems of unification, demobilization, and transitional justice will need to be answered. Meanwhile, someone will have to turn on the lights, pick up the garbage, and reopen the schools.

There would also be enormous economic costs for the region and the United States. Estimates for long-term reconstruction in North Korea top $1 trillion. Don’t expect China or the Europeans to pick up the bill. Colin Powell’s “Pottery Barn” rule of you break it, you own it, would apply. Add to that estimates by the RAND Corporation that a conventional war alone could cost South Korea upwards of 60 percent to 70 percent of its annual gross domestic product, or nearly another trillion dollars.

Finally, America’s prized position in the region would be thrown into disarray, with big outstanding questions about the future of the alliance between the United States and South Korea and the U.S. military presence on the peninsula. Particularly if Washington goes to war against Seoul’s wishes, as would be the case today, it could do irreversible damage to U.S. alliances in Asia and beyond. Further complicating matters, China’s military will almost certainly intervene into a destabilized North Korea, creating both military and political obstacles for the United States. Washington would need a strategy at the ready to advance long-term U.S. interests. Beijing most certainly has one.

There are no indications that the Trump administration has done the necessary preparation for these many challenges, nor has it leveled with the American people about the extraordinary costs the United States would bear if it breaks the North Korean regime. It is imperative that Capitol Hill step up and fill this void before the Trump administration makes any decision to take preventive military action. After more than 16 years of nation building in the Middle East and South Asia, the American people deserve nothing less.

Kelly Magsamen is vice president for national security and international policy at the Center for American Progress.

Ely Ratner is the Maurice Greenberg senior fellow for China studies at the Council on Foreign Relations.