The Korean War of the 1950s was suspended by an armistice rather than a surrender, and over the years there have been exchanges of heated rhetoric and occasional killings across the DMZ. But things have escalated. Pyongyang's third-generation "Dear Leader," Kim Jong Un (son of Kim Jong Il and grandson of Kim Il Sung), has taken displays of terrifying hardware to the next level, most recently this week with his country's highest-ever intercontinental ballistic missile launch. This leaves us all wondering about the prospects of war.

Of course, people have been trying to sort out this kind of thing for millennia, and they've developed just-war criteria for nations contemplating armed conflict. The lists vary in length and cover going to war, conducting war, and following up after war. I'll focus on the first set,  principles for what is called, classically, jus ad bellum ("just entry into war").

Legitimate authority. Check. The United States and the Republic of South Korea are perfectly entitled to take on the North. We're not a bunch of anarchists or mercenaries.

Just cause. Self-defense is a good reason. So, when a foreign leader with nuclear weapons speaks of a "merciless strike" on Guam, Hawaii, or the U.S. mainland, and when that same leader is launching practice missiles over Japan, you pay attention. Besides, if you doubt his will to destroy many people, just look what he's done to his own hapless subjects.

Right intent. The United States and its allies are doing just fine without owning North Korea, its resources, ports, etc. The point is safety and livable peace, not spoils.

Last resort. We're doing what we can through economic sanctions and leverage with China to get him to "stand down." Of course, prior to the enemy's attack, a nation can always ask, "Have we done enough to avert this without ruin to ourselves?" But patience can go too far. Forbearance can slide into appeasement, enabling, and disaster. It's a tough call, and we're doing what we can to get it right.

Probability of success. Here's the rub: No doubt, a dog can kill a skunk, but is it worth it? It all depends upon how one judges success. In this case, if it means the end of a threat to America, the answer is simple. But since Seoul is only a stone's throw from massed artillery, it would be hard to say the war was successful if that city were obliterated.

The quandary is somewhat analogous to the situation where thugs kidnap and threaten to kill a detective's daughter if he pursues an investigation. He can catch them, but at what cost? Or imagine if Hitler had threatened to kill every living person in Luxembourg should the Allies attempt a landing at Normandy. In the end, you have to defeat him; but see "Last resort" above.

Defensive preemption. We've moved beyond the day when you could sufficiently anticipate an attack's timing and location to prepare effectively. In those days, you could deploy your forces as you saw the enemy massing at the border. But now that delivery systems and weapons yields are astonishing in their reach and magnitude, it can be folly to wait for that prompt.

Harvard law professor Alan Dershowitz has distinguished "preemption" (as when the Israelis hit the Egyptian air force on the ground before it could serve up another round of assaults) from "prevention" (something the Allies should have done when Hitler violated the Versailles Treaty and armed his nation to the teeth on the eve of World War II). Arguably, there is a place for both when it comes to North Korea, which has shown little regard for treaties or moderation.

Mark T. Coppenger, a retired infantry officer, is professor of Christian philosophy and ethics at the Southern Baptist Theological Seminary in Louisville, Ky. He is a contributor to the New King James Version Unapologetic Study Bible, from which this article is adapted.