Legislative elections were held in South Korea on 13 April 2016. All 300 members of the National Assembly were elected, 253 from first-past-the-post constituencies and 47 from proportional party lists. The election was an upset victory for the liberal Democratic Party, which defied opinion polling by winning a plurality of seats in the election and defeating the ruling conservative Saenuri Party by one seat. In votes for party lists, however, Democratic Party came third, behind the Saenuri Party in first place and the new People Party in second.
The election marked an upheaval in the South Korean party system, installing a hung parliament for the first time since 2000 and a three-party system for the first time since 1996. The People Party attained a kingmaker position in the new Assembly, while the leadership of the Saenuri Party including chairman Kim Moo-sung resigned en masse following their defeat, relinquishing control of the party to an emergency response commission.
The 2016 legislative election was the first to be held in South Korea following the formation of the People Party and the enforcement of controversial Constitutional Court rulings dissolving the left-wing Unified Progressive Party and mandating the redistricting of the Assembly's constituencies.
Background
In the 2012 legislative election, the ruling conservative Saenuri Party won a slim majority of 152 seats out of 300. The party also retained control of the presidency, as Saenuri candidate Park Geun-hye won the presidential election that year. By the time of the 2016 legislative election, the Saenuri delegation had fallen to 146 out of 292 filled Assembly seats, exactly 50%. The 2016 election was seen as an important stepping stone to the 2017 presidential election, which was held on 9 May 2017.
Redistricting
In 2014, the Constitutional Court of Korea mandated that because the population disparities between the Assembly constituencies were resulting in unequal representation, the constituencies must be redistricted for the 2016 elections. The Court held that the largest and smallest constituencies by population must not differ from each other by more than 2:1, and that the number of constituents in any given constituency must not differ from the average number of constituents by more than one third.
A deadline of 31 December 2015 was set for the redistricting to take place. Nonetheless, by the end of 2015 the National Assembly had not approved a new electoral map. Viewing the situation as an emergency, the National Election Commission was forced to allow registered candidates to campaign without a set map of constituencies. The crisis was ultimately resolved in February 2016 with an agreement between the two major parties that allowed a new electoral map to be passed by the National Assembly. The new set of provisions raised the number of districts from 246 to 253, while decreasing the number of list-selected seats from 54 to 47.
Reordering of the opposition
In the aftermath of the 2013 South Korean sabotage plot, another controversial Constitutional Court ruling enforced the dissolution of the Unified Progressive Party due to the party's alleged ideological affinity to North Korea. The dissolution of the UPP left the Justice Party as the sole left-wing democratic socialist party in the National Assembly. The Korean Confederation of Trade Unions, the most influential democratic trade union organisation in Korea that had originally supported the UPP, now endorsed the Justice Party. The Justice Party's candidates and Assembly members were considered to have similar political views as the left-wing members of the main opposition Democratic Party, and many votes from the Justice Party shifted to the Democratic Party.
The opposition was further fragmented when Ahn Cheol-soo defected from the main opposition Democratic Party and established a new People Party in early 2016. Due to South Korea's largely first-past-the-post electoral system, the division between the liberal Democratic and People parties had led to projections of a sweeping victory for the ruling Saenuri Party in the elections. The two opposition parties considered an electoral alliance but by 5 April the idea was abandoned, with interim Democratic leader Kim Chong-in stating that his party "will hold the elections whether the People’s Party is there or not".