Since North Korea’s artillery barrage targeting a South Korean island last week, concerns have mounted that the incident could escalate into a full-blown military crisis on the Peninsula. The scenario that most experts fear is that North Korea, facing an uncertain leadership succession as dictator Kim Jong-il grows increasingly frail, may be choosing a saber-rattling strategy to gain both attention and concessions from the international community. That thesis was also prominent following the sinking of the South Korean naval vessel Cheonan last spring. Such a strategy, the reasoning goes, although intended to be mere posturing, could lead to miscalculation and tragedy.

U.S. officials understandably focus on the dangers that could arise from North Korea’s actions. But there is a less obvious risk that merits more attention than it has received: that South Korea has had enough of its neighbor’s aggression and may decide to respond in a manner that triggers a crisis. Events over the past week suggest that South Korea’s military and political leadership might be going down that path.

One has come to expect the North Korean propaganda apparatus to spout apocalyptic warnings on a regular basis. Korea watchers have probably lost count of the number of times Pyongyang has threatened to turn Seoul into “a sea of fire” over the years. And predictably, following the latest incident, North Korean media warned that the region teetered on the brink of war, and that both South Korean and U.S. forces would experience dire punishment if such a conflict erupted. There was nothing new in any of this.

What is new—and more than a little ominous—is the tone coming out of South Korea. President Lee Myung-bak thundered that there would be “enormous retaliation” should the North launch another attack like the shelling incident. Presumably, he has something more substantial in mind than the limited economic sanctions that his government imposed following the sinking of the Cheonan. Speaking at the funeral of two South Korean marines killed in the shelling, the commander of those forces vowed “a thousand-fold revenge” for their deaths. Other prominent figures have adopted a similar strident rhetoric.

Of course, this all may be little more than patriotic bluster for domestic consumption. But having staked-out a strong position against Pyongyang’s latest outrage, political and military leaders risk looking weak—indeed, buffoonish—if the actual response is just more ineffectual symbolism. Equally important, the South Korean public seems to be more supportive of serious retaliatory measures than in the past.

During previous crises, many South Koreans worried that Washington’s response to a Pyongyang provocation might plunge the Peninsula into war against the wishes of the South Korean people and government. They had reasons for such fears. In the months leading up to the 1994 Agreed Framework freezing Pyongyang’s plutonium program, the Clinton administration seriously considered air strikes against North Korean targets. South Koreans also remember how Senator John McCain advocated a similar strategy in 2003, and was openly dismissive of possible South Korean objections. Seoul would not have had a veto over U.S. actions in either case, despite the obvious negative consequences.

But now the opposite risk has emerged—that South Korea could drag the United States into an unwanted war. Washington is counseling restraint, and the Obama administration has publicly praised the South Korean government for its patience and prudence to this point. It is more likely than not that U.S. pressure will prevail and cause tempers in Seoul to cool. Yet even if that happens in this case, U.S. policymakers and the American people should soberly assess the grave risks that our country is incurring by maintaining the defense alliance with South Korea and, even more so, by keeping a tripwire military force on the Peninsula.

If Pyongyang continues to prod and provoke its neighbor, at some point South Korean leaders will likely conclude that they must respond militarily. Like the mild- mannered student who is continuously harassed by the playground bully, there often comes a breaking point and that victim takes a stand. In some cases, the bully then backs down and the overall situation improves significantly. But in other cases, a major fight erupts with highly unpredictable results.

If that happens on the Korean Peninsula, Americans will rue the day that their leaders foolishly maintained a military presence in such a dangerous neighborhood.