Timeline: Key developments in North Korea’s nuclear weapons

A North Korean flag flies in the propaganda village of Gijungdong as a US Army soldier stands guard at Taesungdong freedom village, South Korea. AP Photo

A month after shocking the world with its fourth nuclear test, North Korea has followed through with its plans to fire a long-range rocket, defying outside governments that see the launch as a banned test of ballistic missile technology.

Each nuclear test and long-range rocket launch brings the North closer to creating a nuclear warhead small enough to fit on a missile that could strike the mainland United States.

A look at some key developments in North Korea’s nuclear weapons and long-range missile programs.