question: in 2015 Northern Limit Line was written about a war where?
answer: North Korea
context: Title: List of border incidents involving North Korea
  Passage: The following is a list of border incidents involving North and South Korea since the Korean Armistice Agreement of July 27, 1953, ended large scale military action of the Korean War.  Most of these incidents took place near either the Korean Demilitarized Zone or the Northern Limit Line.  This list includes engagements on land, air, and sea, but does not include alleged incursions and terrorist incidents that occurred away from the border.  A total of 3,693 armed North Korean agents have infiltrated into South Korea between 1954 and 1992, with 20% of these occurring between 1967 and 1968.
  Title: Kim Hak-soon
  Passage: Kim Hak-soon (born 1954) is a South Korean film director and screenwriter.  Kim wrote and directed the naval thriller film "Northern Limit Line" (2015) which depicts a real-life naval skirmish with North Korea in June 2002.  It drew more than 6 million viewers 29 days after its release on June 24, 2015, making it one of the top-grossing film in 2015.
  Title: Baengnyeongdo
  Passage: Baengnyeong Island (sometimes spelled Baekryeong; ] ) is a 45.8 km2 , 8.45 km long and 12.56 km wide island in Ongjin County, Incheon, South Korea, located near the Northern Limit Line.  The 1953 Korean Armistice Agreement which ended the Korean War specified that the five islands including Baengnyeong Island would remain under United Nations Command and South Korean control.  This agreement was signed by both the DPRK and the United Nations Command.  Since then, it serves as a maritime demarcation between North and South Korea in the Yellow Sea.  It has a population of approximately 4,329.
  Title: Northern Limit Line
  Passage: The Northern Limit Line or North Limit Line (NLL)-북방한계선(in ROK)- is a disputed maritime demarcation line in the Yellow (West) Sea between the Democratic People's Republic of Korea (DPRK) on the north, and the Republic of Korea (ROK) on the south.  This line of military control acts as the "de facto" maritime boundary between North and South Korea.
  Title: Socheongdo
  Passage: Socheongdo or Socheong Island is a small 5 kilometer long and 3 kilometer wide island in Ongjin County, Incheon, South Korea, located in south Daecheong Island, near the Northern Limit Line.  It is situated in the Yellow Sea, lying 200 km northwest of Incheon, 40 km southwest of the mainland of South Hwanghae, North Korea, and 200 km northeast of Shandong Peninsula, China.
  Title: Northern Limit Line (film)
  Passage: Northern Limit Line () is a 2015 South Korean naval thriller film written and directed by Kim Hak-soon, based on the real-life events of the Second Battle of Yeonpyeong.  It stars Kim Mu-yeol, Jin Goo, and Lee Hyun-woo.
citations: Northern Limit Line (film) Kim Hak-soon