The core belief underlying these assumptions is that North Korea’s supreme leader, Kim Jong-un, is primarily motivated by regime survival and as a consequence would not unnecessarily expose Pyongyang to a U.S. nuclear attack and immediately escalate the conflict to the nuclear level as long as he assumes that he can retain a second-strike capability. Furthermore, under this scenario, Kim assumes that South Korean and American war plans do not entail his removal from power (which, not only due to recent comments by U.S. President Donald Trump, may be a flawed assumption).
The primary objective of the invasion would be to seize Seoul and hold it as long as possible while inflicting maximum damage on the South’s civilian and military infrastructure. Capturing even a portion of the city would not only be an important propaganda victory, but also guarantee the most costly and casualty heavy form of modern warfare to occur on South Korean soil–urban combat.
Assuming that around 70 percent of long-range systems are operational, and factoring in gun crew training (assumed to be mediocre at best) as well as a 15 to 25 percent detonation failure rate of KPA artillery shells, ROK /U.S. forces and civilians in Seoul would still be exposed to a deadly barrage that could kill thousands if not tens of thousands in the first hours of the conflict before KPA artillery is either taken out or has to withdraw due to the fear of being destroyed by counterbattery fire. This analysis also assumes that the KPA will fire chemical shells into Seoul (the North’s chemical weapons stockpile includes mustard gas, sarin, and VX nerve agent) further increasing the chances of mass civilian casualties. The psychological impact of chemical warfare would be immense: One chemical shell exploding in Seoul would be enough to create a civilian mass panic and delay ROK/U.S. forces’ ground movement.
The much debated casualty rate in Seoul will above all depend on the speed of ROK/U.S. counterattacks and the concerted evacuation efforts of Seoul’s civilian authorities.
In addition to artillery strikes, North Korea would launch hundreds of ballistic missiles against civilian targets. (The Diplomat analysis assumes that given the purported inaccuracy of most North Korean ballistic missiles, KPA leadership will use the majority of missiles in countervalue attacks.) The North would not launch its entire ballistic missile arsenal in the initial attack but retain a strike capability for future use. Nevertheless, a salvo of hundreds of conventional ballistic missiles would not only overwhelm ROK and U.S. ballistic missile defense, but would also increase the chance of one of the KPA’s estimated 150 chemical warheads reaching its target — presumably against Seoul. (Other targets might not only include Busan and Incheon but also Tokyo and U.S. military installations in Japan.)
Whether North Korea would succeed in capturing Seoul remains doubtful. From a conventional military perspective, the last decade has seen a decisive shift in favor of the ROK and the United States. It is also far from clear why Kim Jong-un would order such an assault, which would expose a large part of his military (not to mention North Korea’s civilian population) to destruction. The only plausible reason would be that the dictator becomes convinced the United States is on the verge of launching a military campaign against the DPRK. Another explanation related to this is that the North Korean regime sees its nuclear capabilities as the ultimate guarantor of its survival and would be willing to sacrifice a large portion of its conventional strength to preserve its nuclear weapons arsenal, which almost certainly would be the target of U.S. precision strikes in the event of war. Also, North Korea’s military strategy remains focused on reunifying the Korean Peninsula within 30 days of the onset of hostilities, according to open source intelligence.