It was not widely reported, but US approval to South Korea, announced by senior foreign affairs and security secretary Chun Yung-Woo at a news conference, to expand the range of its missiles to 800 km in comparison with the current range limit of 300 km marks a major change in American policy.
Both in Europe and in Southeast Asia, the American preference was to extend an umbrella to its allies in return for the allies' limiting the effectiveness and lethalness of their armaments.
Via this policy, the United States gained greater control over the situation, particularly in terms of dampening down potential arms races (sometimes involving US allies such as Greece and Turkey with a history of tense relations between them) and controlling the dialogue with the main strategic or regional adversary - for example, the Soviet Union. The country accepting the US recommended limitations benefited by not having to increase defense spending.
The permission extended to South Korea means that South Korea can now cover all of North Korea (North Korea already can hit any target in South Korea) but it also places parts of China, Japan and Russia within range.
South Korea is already in a territorial dispute with Japan, another ally of the United States and relations that once seemed to be getting closer have become problematic. While South Korea, thanks to the current hostility between China and Japan, is doing extremely well marketing its vehicles in China and increasing trade with Russia, this doesn't mean that relations will always be rosy.
The US decision signals that as America downsizes its military capabilities, it can no longer offer as extensive an umbrella. In recompense, the United States will have to allow its allies greater leeway in developing military technology and the use of said technology.
As the North Korea nuclear crisis has not been resolved, South Korea and Japan may be motivated to increase their nuclear threshold capability. They both have the technical resources to build nuclear devices and they will now have an effective delivery system in place for when such a decision is reached.