Analysis: North Korea's weakness is its greatest strength. North Korea is kept alive by a drip-feed of aid from China. In theory, control of that lifeline should give Beijing huge leverage over its erstwhile ally. In reality, it does nothing of the sort: if China were to sever the drip-feed North Korea would simply implode, sending millions of refugees into its neighbour and depriving Beijing of what it sees as a vital buffer state against American influence. Once North Korea's scientists have used the rocket to master this long range propulsion system, it could then be used on the Taepodong-2 ballistic missile. This model, now under development, would be able to carry out a nuclear strike as far away as the US. "In technological terms, the launch moves North Korea a major step closer to developing an intercontinental ballistic missile," said James Hardy, from IHS Jane's Defence Weekly. The latest test was, he added, a "significant development in North Korea's pursuit of a nuclear deterrent." Disdainful of sanctions or condemnation, North Korea is the most militarised country in the world, deploying an army almost twice as big as America's with over 1 million soldiers. Only one factor restrains the elite. Their military machine imposes a crushing burden on a wrecked economy, but the North's rulers know they would still lose any war against South Korea and America. Their instinct for self-preservation is all that keeps the peace.