SEOUL – The middle ground between China and the United States is collapsing under South Korea’s feet as it is torn in opposite directions by the two giant economies it seeks to balance between. On the one hand, it is being “requested” to submit detailed information on its flagship industrial sector to the United States – which is also pressuring the country’s number-two memory chipmaker to halt shipments of advanced machinery to China. That move could halt an upgrade to a major DRAM fab, in a sector where large-scale capital investment is crucial. On the other hand, the country’s diesel...