The Korean War broke out in an era of great-power competition. Today’s great-power competition is quite different, but many of the dynamics that turned the Land of the Morning Calm into a battlefield 70 years ago are present now. Thus, the Korean conflict offers important lessons for maintaining stability in today’s world.

Here are the top five.

1. Don't Prioritize Yourself Out of Conventional Deterrence: As the former World War II allies began facing off in a new Cold War, the Pentagon well understood it would be a global struggle. Yet even as the Cold War was heating up, U.S. military budgets were being squeezed to accommodate demands for a domestic “peace dividend.” The Pentagon’s answer was to prioritize American global commitments. Europe, of course, was the main concern, so cuts were made everywhere else. This left the U.S. with a weak post-war occupation force in South Korea. The military chiefs decided that, if war broke out there, we would not fight. As a result, they made no contingency plans for fighting on the peninsula.

When President Truman awoke to news of the North Korea invasion South Korea, he immediately understood the danger of allowing Communist aggression, sanctioned and supported by Moscow, going unchallenged. A U.S. presence in Asia was crucial to global stability. America was on its way to turning Japan, a former enemy, it into a key free world ally—a crucial geostrategic objective. The war in Korea threatened the peace and security of all of Northeast Asia. America had to respond.

Of course, strategists should prioritize and devote the most resources to countering the greatest threat. On the other hand, a good strategy can’t compromise on any meeting any danger that threatens core vital interests. Those risks are not worth taking.

As a global power with global interest and responsibilities, America needs sufficient military power to respond to all of them. During World War II, for example, the allies focused first on the greatest threat—Nazi Germany—but they didn’t stop fighting the war in the Pacific. They balanced commitments. They didn’t neglect them.

This lesson is particularly crucial for facing off in today’s great-power competition. Though China may be the greatest concern, America can’t focus solely on Asia. For one thing, China’s influence and destabilizing activities are global. U.S. counteractions must be global as well.  Further, the U.S. can’t neglect other critical theaters, including Europe and the Greater Middle East; we have critical interests and peace-keeping responsibilities there as well.

2. No More Task Force Smith: When President Truman ordered the American military to help defend South Korea, the Pentagon sent in the closest troops available: occupation forces from Japan. The brigade-size force, called Task Force Smith, lacked the training, readiness and equipment to function as a credible combat unit. They weren’t even a speed bump.

Many folks take the wrong lesson from Task Force Smith. This wasn’t just about being unprepared.  Even if Task Force Smith had been the best-trained brigade in the world, they still would have been crushed by an invading army of overwhelming size.  

Quantity has a quality all its own. It is not just being present that matters. The U.S. must have forces that represent a credible deterrent in all the key places around the world. That means forces that can be protected and reinforced. Potential enemies must know at the front end of a possible conflict there are no cheap, easy wins when the Americans are around.

3. Don't Rob Peter to Pay Paul: Eventually the U.S. deployed sufficient forces to blunt the North Korean invasion. However, they lacked the additional power needed to go on the offensive and liberate the occupied parts of the country. They needed two divisions. At the time, the entire U.S. strategic reserve of active divisions was… two. If the Pentagon sent them to Korea, there was nothing available to reinforce Europe. At great strategic risk, Korea got the extra divisions. Meanwhile, the Pentagon scrambled to build up additional forces to meet global commitments.

Since the end of the Cold War, the U.S. has practiced global sourcing for operations. In other words, they have pulled troops from all around the world to meet contingencies. But that model is not sustainable In today’s great-power competition. Today, the U.S. has to focus on peace and stability in Europe, the Greater Middle East and the Indo-Pacific all at the same time, as well as do other necessary operations around the world and at home (like helping respond to COVID). Nor can the U.S. depend on penny-packets of forces stationed in the U.S. to be deployed like fireman rushed to the scene of the blaze anywhere in the world.

The U.S. has to be concerned that events in one theater will consume so much attention it opens up opportunities for competitors to make mischief elsewhere. Working in concert with friends and allies, the U.S. has to be able to deliver credible conventional deterrence in Europe, the Middle East and the Indo-Pacific simultaneously. If moving stuff around jeopardizes deterrence in any of these areas, then we have a problem.

4. Always Be Prepared to Play Great-Power Politics: North Korea would have never marched South without a greenlight from Stalin. And it wouldn’t have able to survive the war without the armed intervention of China.

Now, there might not be a hidden hand behind every ill will aimed at America today. And, certainly, not all threats are equal. Nevertheless, Washington has to able recognize and respond appropriately to great power threats, in their many shapes and guises. Can we be sure, for example, that out of frustration China might not resort to state-sponsored terrorism and armed surrogates? Who knows? The lesson here is: Don’t be surprised like we were in Korea. 

5. In Great Power Politics, Form Follows Function: In Korea, when the two sides fought to a standstill, the U.S. didn’t sign a peace treaty. That was for a simple reason. There wasn’t peace. There still isn’t. Those who argue we should go ahead and do a peace treaty now—to build trust and confidence—get it backwards.  If we had trust and confidence, signing the treaty would be an afterthought.  

There are no prospects for enduring peace in Korea unless North Korea agrees to stop threatening others. And, unlike 70 years ago, today that means denuclearizing. If North Korea agrees to denuclearize, heck yeah, sign that piece of paper.

In great-power competition, don’t mistake process for progress. Whether it’s arms control treaties or any other measures, first you need to protect and safeguard your interests. Then statecraft can play its important role: working to reach deals of mutual interest that satisfy both sides.

“Smart” diplomacy on its own is no more able to make America safe today than it was during the Cold War. Safety rests in strength. First, demonstrate the capacity to protect your interests. Refuse to compromise on that. Then talk. And, if there is progress, by all means seal the deal.