The initial deployment of a U.S. missile defense system in South Korea has angered both North Korea and China, who views the system as a threat to regional peace.

The Terminal High Altitude Area Defense (THAAD) system is a new missile defense shield specifically designed to intercept short and medium range missiles, destroying them as they near their targets.

THAAD was agreed upon by the U.S. and South Korea last year, and its appearance in South Korea has coincided with an increasingly provocative series of missile tests by North Korea, the latest of which occurred on Monday. Missiles launched by North Korea flew towards Japan, with three of the four landing in the waters that are considered part of Japan’s ‘exclusive economic zone,’ meaning within 200 miles of Japanese territory.

The launches were reportedly personally supervised by North Korean dictator Kim Jong Un, who ordered his military “to keep highly alert as required by the grim situation in which an actual war may break out any time, and get fully ready to promptly move, take positions and strike so that it can open fire to annihilate the enemies.”

Those familiar with the annual interactions between the U.S. and South Korean (ROK) militaries of course know that the North becomes particularly hostile around late winter every year. The U.S. and ROK conduct annual military drills known as Foal Eagle in late February and March every year, and every year North Korea issues a number of threats of varying degree in response.

However, the latest missile launches by North Korea have gone a bit further than the usual annual blustering. Speaking together on Tuesday, President Donald Trump and Japanese Prime Minster Shinzo Abe agreed U.N. resolutions were violated by the missile tests, with Abe saying: “Japan and the U.S. confirmed that the latest North Korean missile launches were clearly against U.N. resolutions and a clear provocation against the regional and international community,” and that “North Korea’s threat has entered a new phase.”

While the U.S. and South Korea have insisted the THAAD missile defense system is a defensive measure to counter the actions of North Korea, China has consistently criticized the system as a direct threat to its own safety.

In accusing the U.S. of increasing tensions with THAAD, China has also accused its nominal ally North Korea of provoking international outrage with its nuclear weapons program.