Chinese President Xi Jingpin elevated the aggressive rhetoric between China and the United States last week when he reportedly told his top military advisers to prepare for war in the South China Sea. The speech, which was made during an inspection tour of China’s Southern Theatre Command, did not directly reference the United States in quotes released by China’s state-owned media outlets, but the target of Xi’s ire seems nonetheless clear.

“It’s necessary to strengthen the mission … and concentrate preparations for fighting a war,” Xi was quoted as saying to his top military leaders about the South China Sea and the region around Taiwan. “We need to take all complex situations into consideration and make emergency plans accordingly. We have to step up combat readiness exercises, joint exercises and confrontational exercises to enhance servicemen’s capabilities and preparation for war.”

Tensions have been increasing between the United States and China in recent years, in large part due to China’s aggressive claims of sovereignty over the entirety of the South China Sea. The waterway, which is the site of competing territorial claims of no fewer than five nations, sees nearly a third of all global commerce shipped across its waves. It also boasts large deposits of natural resources and bountiful fishing territories — making the South China Sea among the most economically important bits of real estate anywhere on the globe.

China’s claims over the South China Sea are, according to Chinese policy, based on a historical precedent. Although other nations have shorelines abutting the South China Sea and international law dictates that their exclusive economic zones should extend 200 nautical miles from their own shores, China’s belief that they have long owned territories throughout the waterway has led them to force foreign nations out of their own territorial waters. This affront to international law has led the United States, the United Kingdom, and several Pacific nations to adopt a confrontational approach to China’s claims in the region — calling them illegal and refusing to acknowledge China’s rule over the territory.