Jeffrey Lewis, a North Korea expert at the Middlebury Institute of International Studies, recalled a 1969 episode in which North Korea shot down a United States Navy plane, killing 31.
The Nixon administration, he said, never retaliated because it could find no options that were “tough enough to punish the North Koreans, but not so tough that the North Koreans will think it’s a general attack,” setting off an all-out war.
That has been the problem ever since, Mr. Lewis said: “News flash, these Venn diagrams do not overlap.”
As North Korea’s nuclear capability has grown, the distance between a single attack and all-out war has shortened. Paradoxically, the heightened fear of escalation also makes it likelier.
“If there were ever a conflict, Pyongyang would have nowhere else to go but up the escalation ladder after artillery except to its nuclear weapons,” Victor Cha, who served as the Asian affairs director on George W. Bush’s National Security Council, wrote in a September column in a South Korean newspaper.
That threat goes both ways, Mr. Cha wrote, because it “compels the United States to pre-emptively attack the nuclear forces at the first sign of conflict.”
A full war, entered deliberately or accidentally, would risk terrible costs.
Gen. Curtis M. Scaparrotti told a congressional committee in 2016, when he was commander of United States forces in South Korea, that war with North Korea “would be more akin to the Korean War and World War II — very complex, probably high casualty.”
Analysts doubt that the United States could reproduce the rapid military victory it achieved against Iraq in 2003. In the event of war, North Korean plans are thought to call for nuclear attacks against major ports and air bases in South Korea and Japan, halting any American invasion before it could fully begin.
In the meantime, nuclear and chemical strikes against major population centers would be intended to shock the world into capitulating. Missile defense would be of limited use against short-range rockets and of no use against North Korea’s hundreds of artillery pieces, many of which target Seoul, the South Korean capital.Seoul has a population density twice that of New York City. Seoul is home to 10 million people. Even an impetuous blowhard like Trump would think twice before sacrificing 10 million people.