Besides the US-ROK joint exercise that the North Koreans are unhappy about, this designation by President Moon might also be why the North Koreans conducted their recent missile test:
The government designated the fourth Friday in March as the Yellow Sea Defense Day to remember those who were killed in waters off the west coast during three battles against North Korea’s provocations in 2002 and 2010.
This year marks the 11th anniversary of two of the three incidents — North Korea’s deadly sinking of the South Korean warship Cheonan on March 26, 2010, and the communist nation’s artillery shelling of Yeonpyeong Island, a front-line island in the Yellow Sea, on Nov. 23, 2010.
Moon said that the government has worked hard to possess “overwhelming” military strength to preserve and create peace.ย
“Not a single soldier has been injured or killed in the past four years in the Yellow Sea due to armed clashes or military provocations. This is proof that a powerful force creates peace,” he said.
The president also highlighted the government’s plan to deploy a light aircraft carrier by 2033 produced by South Korean technology and deploy a 3,000-ton submarine program, which has been in development since 2018, by 2024.
Yonhap
You can read more at the link, but I was a bit surprised that the Moon administration actually made this designation considering their default appeasement policy towards North Korea. Plus many in the Korean left still believe that North Korea did not sink the Cheonan.
By the way there has been far more incidents than just the sinking of the Cheonan and the Yeonpyeong Island shelling in the Yellow Sea. The 2002 West Sea Naval Battle was another major deadly clash in these waters:
