There is a lot of movement right now happening under the radar screen between China and the Koreas. Before Trump became president South Korea changed leaders to one who is now infamous for kowtowing to China.
What is really happening behind the scenes is China is playing the geopolitical chessboard to bring about a Korean peninsula that it wants to see and that is one that is completely dominated by the Communist Party of China. How is this best achieved? By getting the U.S. military out of South Korea.