A House Divided: Photos From Korea’s 1948 Yeosu-Suncheon Rebellion

Two years before the Korean peninsula erupted in a civil war that saw the North and the South (and the U.S., the United Nations, the Soviet Union and China) engage in a conflict that shaped the post-World War II world, a short, brutal rebellion in the young Korean republic paved the way for the cataclysmic Korean War to come. The Yeosu-Suncheon Rebellion, as it came to be called, took place in October 1948, when communist rebels — many of whom had been in the American-trained Korean Army — revolted against the (authoritarian) government of President Syngman Rhee.

As tensions on the peninsula again reach a boiling point and as the rhetoric from both sides — especially from the North’s young, largely untested leader, Kim Jong Un — grows more belligerent and more bizarre, the Yeosu-Suncheon Rebellion might seem like little more than a historical anomaly: a minor, forgettable blip in Asia’s long, fraught history.

But in cultures that measure their histories in terms of millennia, rather than decades or even centuries, a revolt and its repression is not merely remembered seven decades later; instead, it helps inform every utterance, every threat, every gesture emanating from South Korea and North Korea today.

Here, in an effort to perhaps add some needed context to the current situation on either side of the 38th parallel, LIFE.com presents a series of photos by the great Carl Mydans, who was on the ground when the rebellion began, and bore witness to the carnage that followed. Most of these pictures never ran in LIFE magazine. (We should also note that the Yeosu-Suncheon Rebellion came on the heels of the South Korean army’s notoriously violent suppression of an uprising on the island of Jeju, off the southern coast of Korea, in April 1948.)

[See all of TIME.com’s Korea coverage.]

In November 1948, in an article titled, “A New Communist Uprising Turns Men Into Butchers,” LIFE painted an unsettling picture of the rebellion, complete with the observation that the United States “gave South Korea a government” after the Second World War — suggesting, unintentionally perhaps, that the Korean peninsula was once again little more than a convenient crossroads upon which more powerful nations have always fought their proxy wars.

In type-written notes sent to LIFE’s editors on October 24, 1948, Mydans was even more plainspoken about the terrors he and three other correspondents (see the photo above) witnessed during the rebellion and its suppression. “Covering this war is difficult and frightening,” he wrote. “Both factions in the fight wear the same uniform, ride in the same American vehicles and are armed with the same weapons. . . . Tonight as I write this in the hillside home of [Presbyterian missionary] Dr. Crane the reports of rifles and automatic weapons still sound nearby and to we four correspondents it carries the full feeling of war.”

“We entered Sunchon 1 PM on the 24th,” he continued. “The city stank of death and was ill with the marks of horror.”

Almost plaintively — but with never a hint of self-pity or complaint — Mydans also noted that “it is now midnight and we haven’t been to bed for two days. . . . We [he and the three other newsmen] are all the outside observers there are of this point in Korean history.”

— Ben Cosgrove is the Editor of LIFE.com