Why is South Korea holding a presidential election? What are the big issues in South Korea's election? Yoon's martial law laid bare the deep political divisions in the country, as those who supported his decision to impose martial law and those who opposed it took to the streets in protest. South Korea's new leader must also balance Seoul's relations between its biggest trading partner, Beijing, and its most important security ally, Washington. Before the election, Yoon quit his party in what analysts said was an attempt to shore up the chances of PPP's presidential candidate Kim Moon-soo.