Background and causes
The background to the coup can be analysed both in terms of its immediate context, and the broader setting of the development post-liberation South Korea. While the Second Republic presented South Korea with a singularly problematic economic and political climate which encouraged a military intervention, the direct roots of the coup stretch back to the late Rhee period, and more recent historians such as Yong-Sup Han argue that the frequently recurring image of the coup as an inevitable direct response purely to the vagaries of a new regime paralyzed by endemic instability is over-simplistic.
South Korea under Syngman Rhee
From 1948, South Korea was governed by President Syngman Rhee, an anti-Communist who used the Korean War to consolidate a monopoly on political power in the republic. Rhee represented the interests of a conservative ruling class, the so-called "liberation aristocrats" who had risen to positions of influence under American occupation. These "liberation aristocrats" formed the bulk of the political class, encompassing both Rhee's supporters and his rivals in the Democratic Party, which advanced a vision of society broadly similar to his own. Rhee eliminated any significant source of real opposition, securing for example the execution of Cho Bong-am, who had campaigned against him in the presidential elections of 1956 on a platform of peaceful reunification and had attracted some 30% of the vote, an unacceptably high level of support for an opposition candidate.
Even such significant opposition figures as Cho, however, can be considered to have been part of the broad conservative consensus of the governing class, which rested on a traditionalist, Confucian worldview that saw "pluralism in ideology and equality in human relationships [as] foreign concepts", and which upheld the value of paternalist government and the power of extensive networks of political patronage. Rhee, under this traditionalist model, was the foremost "elder" in Korean society, to whom Koreans owed familial allegiance, and this relationship was strengthened by the ties of obligation that connected Rhee to many in the ruling class.
One result of the rule of the "liberation aristocrats" was the stalling of development in South Korea, in marked contrast to the situation in nearby Japan. Where South Korea had been intensively developed under the Japanese colonial system, Rhee's presidency saw little significant effort to develop the South Korean economy, which remained stagnant, poor and largely agrarian. The lack of development under Rhee provoked a growing nationalistic intellectual reaction which called for a radical restructuring of society and a thorough political and economic reorganization, rejecting the American model being pursued by the governing elite. Park Chung-hee, the later leader of the May Coup who at that time was a second-tier army officer with decidedly ambiguous political leanings, was heavily influenced by this unfolding intellectual reaction.
Social and economic problems of the Second Republic
After rigged elections in March 1960, growing protests developed into the April Revolution, and Rhee was pressured by the United States into a peaceful resignation on April 26. With Rhee out of the way, a new constitution was promulgated establishing the Second Republic, and legislative elections on June 29 resulted in a landslide victory for the Democratic Party, with Rhee's Liberals reduced to a mere two seats in the newly constituted lower house of the National Assembly. The Democrat Yun Bo-seon was elected as figurehead president in August, and Chang Myon, former Vice-President, took over as Prime Minister with executive authority under the parliamentary republican system established by the new constitution.
The Second Republic was beset with problems from the start, with bitter factionalism in the ruling Democratic Party competing with implacable popular unrest for the government's attention. The South Korean economy deteriorated under heavy inflation and high rates of unemployment, while recorded crime rates more than doubled; from December 1960 to April 1961, for example, the price of rice increased by 60 percent, while unemployment remained above 23%. Widespread food shortages resulted. Chang Myon, meanwhile, representing the Democratic Party's "New Faction", had been elected Prime Minister by the thin margin of three votes. Purges of Rhee's appointees were rendered ineffective in the public eye by Chang's manipulation of the suspect list to favour wealthy businessmen and powerful generals. Although Rhee had been removed and a democratic constitution instituted, the "liberation aristocrats" remained in power, and the worsening problems facing South Korea were proving insurmountable for the new government.
The breakdown of South Korean politics and the administrative purges racking the army combined to demoralise and discourage the Military Security Command, which was charged with the maintenance of the chain of command in the military and weeding out insubordination. The reluctance of the Military Security Command to act allowed plans for a coup to unfold, and so the problems of the Second Republic not only provided a justification and an intellectual movement for a coup, but also directly enabled the coup to be organised and realised.
Factionalism in the military
A direct factor in paving the way to the coup was factionalism in the South Korean army itself, one of the largest in the world at the time with 600,000 soldiers. The army had been given a distinctive identity by the dual Japanese and subsequently American training that many of its members had received, "combin[ing] the Japanese militarist ethos with the American spirit of technical efficiency to expand its mission from defending the country against communist aggression to that of helping it build itself into a modern nation". Reformist junior officers viewed the senior generals as having been corrupted by party politics, and the problem was compounded by a bottleneck in promotions caused by the consolidation of the positions of the senior commanders of the army after the end of its rapid expansion in the Korean War.
The army was also divided along regional lines and between factions of officers who had graduated from the same school. Of the latter, the most influential were the competing factions who had graduated from the Japanese Military Academy and from the Manchurian officers' school at Xinjing respectively, while more lower-ranked officers were divided by their class of graduation from the post-liberation Korean Military Academy. Park Chung-hee had attended all three institutions, and was uniquely positioned to lead what would become the coup coalition, with his extensive ties among both the senior commanders of the army and the younger factions.
After the overthrow of the Rhee regime and the institution of the Second Republic, the reformists, led by KMA alumni, began to call for the senior commanders to be held to account for complicity in the rigging of the 1960 and 1956 presidential elections. Park Chung-hee, relatively high-ranking as Major General, threw himself into the spotlight by declaring his support for the reformists and demanding the resignation of Army Chief of Staff Song Yo-chan on May 2. On September 24, sixteen colonels, led by Kim Jong-pil, demanded the resignation of Chairman of the Joint Chiefs of Staff
Choi Yong-hui in an incident known as the "revolt against seniors" (Hangul: 하극상 사건; Hanja: 下剋上事件; RR: hageuksang sageon). By this point, initial plans for a coup were already advanced, and the "revolt against seniors" removed an important potential enemy.