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.”