North Korea has developed a nuclear weapons program despite poverty and international sanctions, using home-grown technology and virtually free labor to cut costs, experts said.
An analysis by the South Korean government has put North Korea's nuclear spending at $1.1 billion to $3.2 billion overall, although experts say it is impossible to make an accurate calculation given the secrecy surrounding the program, and estimates vary widely.
However, the weapons that North Korea has tested thus far are comparatively small and based mostly on less sophisticated fission, or atomic bomb, technology.