With inter-Korean tensions high and a key military agreement increasingly at risk, a shootout on Monday morning provided a reminder of why the waters of the Yellow Sea could spark the next crisis on the peninsula.

Early in the morning, South Korea said it fired warning shots after a North Korean merchant ship strayed into its territorial waters. The DPRK maintained that the South’s claims were just an “excuse” and sent a “grave warning” against two ROK ships that it said intruded into its waters.