Why does China react so strongly over the South Korea-based anti-missile system?
China concerned about the potential threat from defence network in its backyard

Beijing has issued a rare strong rebuke to Seoul over its decision this week to restart talks with the United States over deploying a defence system designed to shoot down ballistic missiles.
Ostensibly, the Terminal High Altitude Area Defence System (THAAD) developed by the US is meant to neutralise missile threats from North Korea. But given China’s open condemnation of Pyongyang’s nuclear antics, Beijing’s strong reaction to the deployment of THAAD may look out of place.
Chinese military observers said Beijing’s response reflected concerns the system would view the PLA’s operations over the Taiwan Strait and the South China Sea in greater detail and eventually further unite South Korea, Japan and the US in a defence alliance.
With radars that can reach up to 4,000km away, a THAAD system based in South Korea would severely compromise China’s controversial air defence zone.
They also warned that the system could prompt China and Russia to stockpile ballistic missiles and deploy more nuclear-powered submarines as counterbalances.
