Accidental wars rarely happen. Historians have demonstrated that most wars initially deemed “accidental,” (perhaps most notably the First World War), have in actuality resulted from deliberative state policy, even if the circumstances of the war were unplanned. While war seems discordant, it actually requires a great deal of cooperation and coordination. Fundamentally, two parties have to agree to conduct a war; otherwise, you have either a punitive raid or an armed surrender negotiation.
Consequently, the baseline for evaluating the chances for accidental war on the Korean Peninsula should be judged as quite low. South Korea, in all likelihood, views the prospect of decisive victory against North Korea as worse than the status quo. The United States has no interest in fighting a war against the DPRK at the moment. For example, the sinking of the Cheonan was obviously an act of war, but neither the United States nor South Korea were interested in fighting a war on the terms offered. While we know less about the strategic calculus of North Korea, there is little reason to think that North Korea was interested in war, either; it probed South Korean capabilities and resolve, but did not press the issue in ways that could have forced Seoul’s hand.
This said, there are conditions under which the chances for accidental wars increase. If the main parties do not communicate well (or at all) with one another, they may misunderstand messages designed to convey commitment or capability. Cultural differences can contribute to a lack of appreciation of how a potential foe thinks about the costs and benefits of war. Domestic conflict invariably complicates foreign policy, as state leaders often act according to a logic that places the dictata of their governing coalitions above foreign policy concerns. Finally, leaders do not have full control over their military organizations; a rogue artillery commander, fighter pilot, or sub skipper can effectively initiate hostilities on their own. All of these conditions can lead to situations in which states commit what they believe is limited force in service of what they believe are limited objectives, but in actuality threatens core interests of the enemy.
The potential for accidental war is highest in conditions where technology and doctrine overwhelmingly favor quick, offensive action, and produce quick, decisive outcomes. Wars that could de-escalate following a border skirmish and a few artillery duels can escalate beyond control if both sides understand the timing of offensive action to be critical. Arguably, the conditions on the Korean Peninsula currently match this description. Although there’s virtually no scenario in which North Korea could win a war, if allowed to mobilize and launch well prepared, coordinate offensive activities the DPRK could inflict severe damage on the South Korean military and South Korean civilians.
Similarly, a pre-emptive U.S.-ROK assault on the North Korean military, or an attack launched in the very early stages of a North Korean assault, could substantially undercut the power of North Korea’s first punch.
Such an operation would include a wide array of attacks, launched from sea, air, and land platforms, targeting North Korean airfields, communication nodes, and logistic chokepoints. These attacks would attempt to eliminate North Korean offensive capabilities, especially for direct attacks against the South (and presumably against Japan). The ability of the DPRK to provide any defense against a committed air offensive is in deep question, despite a large air force and an extensive SAM network. North Korea is the war that the U.S. Air Force (USAF) (and to a lesser extent, the U.S. Navy) have been dreaming about fighting since the 1970s, and they remain well prepared to fight it. The last major armored offensive to push forward under a condition of enemy air supremacy was the North Vietnamese Easter Offensive of 1972, which ended in disaster; the North Koreans would operate under considerably greater handicap.
The North Korean nuclear program exacerbates these difficulties. If the ROK and United States decided to launch a preemptive strike, DPRK nuclear sites would be among their first targets. The ability of U.S. and South Korean intelligence to successfully identify these targets (and to assess their destruction at high levels of confidence) remains highly questionable, but North Korea might nevertheless decide that it needs to use the weapons in some fashion in order to preserve the strategic and political balance. Whether the use of weapons would prevent regime destruction is a different question entirely; the senior military and political leadership may assess the weapons as regime saviors, even if a nuclear detonation would ensure the resolve of South Korea and the U.S. to end the DPRK.