During the first two decades of his leadership, Kim Il Sung had yet to fully consolidate his power at the head of the government. The two major threats to his premiership came in 1956 and 1967 at the hands of his political opponents, and later, his close allies. The first attempted failed and resulted in Kim re-firming support for his leadership among the political elite and the public at large. The second attempt allowed the Premier to secure his dominance within the Worker's Party and consolidate his position at its head.
In the early years of the DPRK after its formation in 1948 and recovery from the Victorius Fatherland Liberation War (Korean War), the political class in Pyongyang was divided into 4 distinct groups:
Kim Il Sung led the Kapsan faction [갑산파] which consisted of veterans from the anti-japanese guerilla forces which Kim had commanded against the Japanese during their occupation of Korea in the early 20th century.
The Yan'an faction [연안파] was made up of pro-China communist politicians who had lived in exile in China. Numerous faction members had served in the Chinese military and thus cultivated a close relationshiop with Mao and his government.
The Communist faction, also known as the Domestic faction, consisted primarily of Korean communists who remained on the peninsula during the Japanese occupation, many of whom were imprisoned for the anti-occupation activities.
The Korean-Soviet faction members were ethnic Koreans who had been born or raised in the Soviet Union. Many had been members of the Red Army or worked covertly in Korea during the occupation.
In the years following the Korean War, Kim Il Sung moved to secure his authority over the Communist faction. Leading figures in the Communist movement were purged including Pak Hon Yong [박헌영], leader of the Communist Party of Korea. It was Kim Il Sung's de-facto domination of the Workers' Party of Korea which eventually led to his first major internal challenge, the August Faction Incident.
In 1956 the Soviet and Yan'an factions planned to move against Kim Il Sung at a plenum of the Central Committee of the Workers' Party. Kim Il Sung was in Moscow prior to the plenum to meet with new Soviet Premier Nikita Krushchev who had recently denounced his predecessor, Josef Stalin, for employing political tactics similar to those used by Kim Il Sung. For this reason, the coup had the support of Moscow who hoped a reformist politician would take over control of the party. The Chinese also supported Kim Il Sung's removal through their tacit support for the Yan'an faction. Upon his return to Pyongyang, Kim delayed the plenum for 6 weeks allowing for time to make back-room agreements with central committee members in order to stage a dramatic response to the plotters. Choe Chang Ik and Yun Kong Hum led the charge attacking Kim for concentrating power and creating a 'police state'. These speeches were drowned out by supporters of the Kapsan Faction who moved to expel Yun from the party. Kim Il Sung's response resulted in him winning the support of his peers in the Central Committee and the leaders of the failed coup were expelled from the party leadership.
What followed was a political purge on a scale as yet unseen in North Korean politics in which members of the Yan'an and Soviet factions were removed from political positions. The purge went so far as to remove the nominal head of state, President Kim Tu Bong, from power in 1958. In July 1959, a by-election was held to elect deputies to the Supreme People's Assembly after a quarter of the previous deputies had been purged.
By the end of the 1950s the Yan'an, Communist and Soviet factions had been all but eliminated and no longer commanded any real power within the party. The Kapsan faction was now the dominant party-political force within the WPK and was initially close to Kim Il Sung. However, in the aftermath of the 1966 Conference of the Workers' Party of Korea the faction began to challenge Kim on economic reform. The faction elevated Pak Kum Chol as a potential successor to Kim Il Sung and began to exalte his words as 'teachings', rivalling those of Kim. Pak overstepped the mark when he began to openly criticise Kim and his policies which resulted in an official warning from the increasingly frustrated Kim Il Sung against factionalism. During a meeting with party loyalists it was agreed that the Kapsan faction should be ousted. Over 100 faction members were formally expelled from the party and many high level plotters disappeared from the public eye. The investigation that followed was headed by Kim Jong Il, son and later successor of Kim Il Sung. This was the first official party-political duty delegated to him by his father.
While the August Faction Incident is notable for being the moment Pyongyang gained full political autonomy from the USSR and China, the Kapsan Incident is considered to be the start of the current political system in the country since there has not been a credible leadership challenge against the Supreme Leader of the DPRK since 1967.