Alek Chance is a research fellow and program coordinator with the Washington-based Institute for China-American Studies.
He says the decision to deploy the system is already starting to have repurcussions in the region.
"It is certainly a change to the status quo that has raised a lot of eyebrows and raised very serious concerns with China and with Russia, and has drawn very negative reaction from North Korea of course. So an alteration of the status quo like that is, to some degree, destabilizing."
The Terminal High-Altitute Area Defense system, THAAD, is designed to intercept short and intermediate-range ballistic missiles.
In order to be effective, it has to have significant radar coverage.
This is a major concern for both China and Russia, as the radar range will include both Chinese and Russian territory.
Alek Chance says while the THAAD system is designed for regional missile protection, its capabilities impact both Chinese and Russian nuclear deterence options.
"A THAAD battery in South Korea could not strike down any Chinese or Russian inter-continental ballistic missiles that were launched at the United States. It could not do that. It probably can't look as far into China as some Chinese reports suggest, I have read estimates looking at something like 1,500 kilometers. However, it can watch missile trajectories that are launched from eastern China and potentially from some parts in eastern Russia and feed information into other radar systems and ballistic missile defense systems."
The U.S. and South Korea have announced plans to deploy the THAAD system in Seongju County, which is around 300-kilometers southeast of Seoul, before the end of next year.
It's a decision which has already prompted strong protests within the county itself, but has also drawn a strong rebuke from both the Chinese and Russian governments.
Despite this, South Korean President Park Geun-hye insists the THAAD system is essential for South Korea's protection from ballistic missile launches from North Korea.
She also says the decision to deploy the system is -quote- "irreversable."
For CRI, I'm Xie Cheng.
