The WPSK launched an insurgency in April 1948, attacking police and Northwest Youth League members stationed on Jeju who had been mobilized to suppress the protests by force.

[1]: 166–167 [6] The First Republic of Korea under President Syngman Rhee escalated the suppression of the uprising from August 1948, declaring martial law in November and beginning an "eradication campaign" against rebel forces in the rural areas of Jeju in March 1949, defeating them within two months.

Many rebel veterans and suspected sympathizers were later killed upon the outbreak of the Korean War in June 1950, and the existence of the Jeju uprising was officially censored and repressed in South Korea for several decades.

As with the mainland, the period immediately following the Japanese surrender was characterized by the formation of People's Committees, local autonomous councils tasked with coordinating the transition towards Korean independence.

[18]: 17–18  However, since the 2000s, many South Korean liberal scholars and bereaved families of the victims of the massacre have evaluated that the Jeju People's Committee has nothing to do with directive of the WPSK.

[1] Although both the police and paramilitary groups employed violent and harsh tactics in their suppression of the locals, the Northwest Youth League was especially ruthless, described as borderline terroristic.

Some sources claim it came about when military police "fired on a demonstration commemorating the Korean struggle against Japanese rule," igniting mass insurrection.

[1][6] Lieutenant General Kim Ik-ryeol, commander of police forces on the island, attempted to end the insurrection peacefully by negotiating with the rebels.

The US military government responded to guerrilla activity by transferring another regiment to Jeju from Busan and deploying police companies, each 1,700 strong, from the southern provinces of the mainland.

In response, US military provincial governor William F. Dean ordered a purge of WPSK sympathizers from the ranks of the Korean constabulary, and three sergeants were summarily executed.

[22] During election week, the guerrillas "cut telephone lines, destroyed bridges, and blocked roads with piles of stones to disrupt communications.

"[1] The WPSK Women's League campaigned for residents to hide in the mountainous region controlled by guerillas the night before the election so they could not be brought out to vote at gunpoint, and thousands did.

[1][7] Fearing an upsurge in guerrilla activities after they succeeded in getting what they wanted out of the election, General Dean requested a US Navy blockade of the island on May 11, so that sympathizers from the mainland could not reach Jeju.

[1] Although guerrilla activities waned during the summer months of 1948, they picked up again in August after the Soviet Union held elections north of the 38th parallel to form the Democratic People's Republic of Korea (DPRK).

[1][6] In the months following the elections, conditions worsened to the point that Republic of Korea (ROK) officials decided to send the Fourteenth Regiment of the Korean Constabulary, stationed near the southern port city of Yeosu, to Jeju Island to assist counter-guerrilla efforts.

[1][7]: 34  Embarrassed by this incident, Syngman Rhee, the newly elected president of the ROK, intensified the government's efforts to stamp out the rebellion.

They summarized that the February 1948 Jeju general strike prior to the rebellion was caused by instigation by the WPSK and hostility towards the police as a result of shootings.

[12] By the spring of 1949 four South Korean Army battalions arrived and joined the local constabulary, police forces, and right-wing Northwest Youth Association partisans to suppress protests.

On August 30, 1950, a written order by a senior intelligence officer in the South Korean Navy instructed Jeju's police to "execute all those in groups C and D by firing squad no later than September 6.

In 1992, President Roh Tae Woo's government sealed up a cave on Mount Halla, where the remains of massacre victims had been discovered.

[31] In 2003, the National Committee for Investigation of the Truth about the Jeju April 3 Incident chaired by South Korean prime minister Goh Kun described the event as a genocide.

"[13] In March 2009, the Truth and Reconciliation Commission revealed, "At least 20,000 people jailed for taking part in the popular uprisings in Jeju, Yeosu and Suncheon, accused of being communists, were massacred in some 20 prisons across the country," when the Korean War broke out.

The first published recollection in South Korea of the massacre was the 1978 novel Sun-i Samch'on (Korean: 순이삼촌, "Uncle Suni") which is set during the event.

However, it was swiftly banned by the ROK government and its author, Hyun Ki-young, was arrested and tortured for three days by the National Intelligence Service.

"[39] On December 26, 1999, the National Assembly passed a bill, 'A special law for the Jeju uprising truth ascertainment and the regaining impaired reputation of the victims'.

[39] In line with the finding of the committee, on October 31, 2003, former president Roh Moo-hyeon admitted that the brutal suppression of the uprising was a massive abuse of governmental power and made a public apology to the people of Jeju on behalf of the Republic of Korea.

On the 71st anniversary of the event, the defense ministry and police under the Moon Jae-in administration apologized for the past government's role in the Jeju massacre.

Kim Gwang-dong, the director of researching policy in Korea argued that though the fundamental characteristic of the uprising was "subversion of the system," there were many skewed and biased studies that criticized the Korean government's faults in suppressing the rebellion.

"[41] A Presbyterian minister, Lee Jong-yoon, said at a church in Seoul that "the Jeju rising was incurred by the leftist forces and they provoked the rebellion to disturb the May 10 general election."

[42] On November 20, 2010, a chairman of an adjustment committee of past affairs and a former new right, Lee Young-Jo argued that the "Jeju rising was apparent communist-led rebellion.