North Korean weapons engineers have done remarkable work with remarkably little. Fortunately, North Korea has been largely cut off from the international arms market for a long time, even from suppliers such as China and Russia. While North Korean industry is not primitive, it cannot support the development of multiple modern military systems. South Korea, on the other hand, has taken great advantage of the international arms market, acquiring technology from foreign powers, defraying costs through joint projects, and exporting weapons in order to earn hard cash and create economies of scale.
If North Korea somehow regained access to these markets, and if it could manage the resources necessary to acquiring new weapons, what would it want?
S-400
As much as anything, North Korea requires an integrated air defense network that can identify and defeat incoming threats. At present, North Korea sports an air defense network that combines imported Soviet technology [3] (mostly from the 1960s) with indigenously developed equipment. In combination with dense anti-aircraft artillery and a variety of small, portable systems, this network could give the United States pause, if not seriously pose a threat to U.S. airpower.