American soldiers on Korea's western front on Christmas Eve, 1951AP

In the late summer of 1950, the United States made a momentous choice—one that, in the end, may have transformed a prospective military and diplomatic triumph into disaster.

The choice was made during what is now often called “the forgotten war”—the three-year conflict in Korea at the outset of the Cold War. But the fall of 1950 has an urgent lesson to teach the U.S. today, as it faces a mounting crisis over the threat of the Islamic State in the Middle East and now in Europe. Choices the U.S. makes, or don’t make, now can have profound effects later.

In 1950, U.S. officials chose to send U.S. forces across the 38th parallel and up the coast of Korea, in pursuit of the fleeing North Korean People’s Army (NKPA), all the way to the Yalu River and the perilous northeast dividing line where the territory of North Korea, China, and the Soviet Union meet.

After North Korea invaded the South in June, the U.S. rushed ill-prepared troops to oppose them. But U.S. forces (and soon the United Nations under U.S. command) were nearly driven into the sea.

General Douglas MacArthur designed a brilliant amphibious landing on the west coast of Korea near Seoul, and within a few days of battle the NKPA began to flee northward.

But success raised a question: What were the allies fighting for? The 38th parallel had been the dividing line between North and South. Soon that status quo would be restored. What should the U.S. do then?

The U.S. could pause and propose a cease-fire. It could pursue the NKPA in order to capture and disarm it, then withdraw. It could occupy North Korea and proclaim a unified Republic in the entire peninsula. Or it could drive on to the Yalu.

A few voices in Washington warned that the drive to the Chinese border was risky. The Chinese, through diplomatic sources, said that an advance on the Yalu would bring them into the war. U.S. military leaders, under the influence of MacArthur, belittled China’s determination and capabilities. The troops rolled on toward the Yalu—with no clear announcement of why they were going there or what they would do.

A few weeks later, Chinese “volunteers” poured over the border, catching U.N. forces by surprise. MacArthur had publicly promised GIs that they would be “home for Christmas.” But they were pushed back down the peninsula to a shaky truce line near the parallel—where they held, fighting a bitter shadow war while generals tried to negotiate a settlement. Eight thousand five hundred Americans had died in Korea before the Chinese intervention. More than three times that number died in the next two years.

In retrospect, it’s not clear which choice would have been the correct one. Pausing at the border might simply have allowed the NKPA to regroup and attack again. Occupation might have been costly, and installing the Rhee government in the North—already criticized for its autocratic ways—might have destroyed the unity and legitimacy of the U.N. effort. And proceeding directly north posed a threat of war with China.

But what should concern Americans today is that a handful of powerful men in the U.S. military and the White House made the decision. The National Security Council warred with the Joint Chiefs of Staff about limits on the military once it entered the North; MacArthur seemed to have his own, more expansive ideas. U.S. allies expressed concern through diplomatic channels; but at no time was there a public debate.

The U.S. military action was taken under United Nations Security Council Resolution 83, which called on member states to “furnish such assistance to the Republic of Korea as may be necessary to repel the armed attack and to restore international peace and security in the area.” Whatever that meant, it was the only public statement of American war aims.

Congress had not been asked neither when U.S. troops were sent into the war in June 1950, nor when U.N. forces crossed the parallel in October.  The White House ordered troops and materiel into the fight without even consulting congressional leaders. A few old Washington hands—such as Ambassador Averell Harriman—urged President Harry Truman to seek formal authorization from Congress. Some Republican leaders, like Senators Robert A. Taft of Ohio and Kenneth Wherry of Wisconsin, asked him to follow constitutional procedures; but others, like Senators Scott Lucas of Illinois and Tom Connally of Texas, opposed such a move. So did Secretary of State Dean Acheson. The fear was that an open debate would allow the far-right, McCarthy wing of the Republican Party to air their charges of incompetence and treason, sending a message of internal division at a time when unity seemed to be needed. Besides, the people were united—everyone believed that the aggression should be stopped.

The failure to obtain authorization is often cited as having cost Truman politically when, after the Chinese invasion, the war turned bitter. Constitutional lawyers, like me, often caution presidents that public support can be fickle. That’s the argument advanced by my colleague Conor Friedersdorf here, quoting Ilya Somin in The Washington Post:

One of the main justifications for the Constitution’s requirement that presidents can only initiate war if they have congressional authorization is to ensure that any such war is backed by a broad political consensus. If we decide to fight a war at all, it should only be in cases where there is widespread agreement that the war is justified, and that we will do what is necessary to prevail.

I agree. But the truth is, most wars, declared or undeclared, are popular at the outset and unpopular if they drag on. George W. Bush got his authorization for the war in Iraq in 2002; that didn’t stop the public, and the politicians, from jumping ship when the war turned out to be a disaster.

The U.S. has been conducting, and expanding, military operations in the Middle East for more than a year without a serious debate. After the atrocities in Syria, the bombing of a Russian airliner, the suicide bombings in Lebanon and Iraq, and the massacre in Paris, the world, and the American people, demand that the U.S. step up the war, if that’s what it is, against ISIS.

A congressional war debate may be important not as a show of national unity but to highlight disunity. Now, not later, is the time to explore the gap between those, like President Obama, who want to fight a measured war against ISIS, and those across the aisle who want to declare war on “radical Islam,” or proclaim “a clash of civilizations.”

A “war” against ISIS will be hard enough. The “enemy” is a non-state actor; there’s so little information that it’s difficult to agree, from day to day, on what its name is. How will the U.S. know how to defeat it? How can the country keep the war from spreading into an unwinnable assault on a religion or a civilization? Is the U.S. preparing to fight, in Joe Haldeman’s phrase, a “forever war”?

Perhaps politics are completely broken and a debate will do no good. But if  U.S. leaders can’t decide between “leading from behind” and plunging into a global religious war, perhaps the country shouldn’t be sending its young men and women to risk their lives.

And there’s always a chance airing differences will help reduce them. It could happen. Besides, America’s fundamental law says it should. Surely that counts for something.

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