South Korea and the US have reached a new deal allowing South Korea to develop tactical ballistic missiles able to deliver a 500kg warhead a distance of 300 kilometers. The US is concerned that unrestricted missile development by a US ally that is hosting US troops could cause regional instability and political embarrassment. If South Korea deployed a missile type that the US did not think North Korea should have, the US would have no credibility in its demands for North Korean compliance. The new limits are those of the Missile Technology Control Regime.--Stephen V Cole