Leaders of China and South Korea called Wednesday for a boost in relations on the 30th anniversary of the normalization of diplomatic ties, as Seoul faces a delicate balancing act between its security ally, the United States, and its largest trading partner.South Korean President Yoon Suk Yeol and Chinese President Xi Jinping exchanged congratulatory letters, with Yoon expressing hope that "new ways of cooperation" can be found over the next 30 years and Xi calling for "a substantive friendship" with the anniversary as the new starting point, the South Korean presidential office said.Xi poi…READ FULL ARTICLE