<Tr> <Td> Location of North Korea's Nuclear tests 1: 2006; 2: 2009; 3: 2013; 4: 2016 / 1; 5: 2016 / 9; 6: 2017; V </Td> </Tr> <P> This chronology of the North Korean nuclear program has its roots in the 1950s and begins in earnest in 1989 with the end of the Cold War and the collapse of the Soviet Union, the main economic ally of North Korea . The Chronology mainly addresses the conflict between the United States and North Korea, while including the influences of the other members of the six - party talks: China, Russia, South Korea, and Japan . </P> <P> The North Korean nuclear program can roughly be divided into four phases . Phase I (1956--80) dealt primarily with training and gaining basic knowledge . Phase II (1980--94) covers the growth and eventual suspension of North Korea's domestic plutonium production program . Phase III (1994--2002) covers the period of the "freeze" on North Korea's plutonium program (though North Korea pursued uranium enrichment in secret) and Phase IV (2002--present) covers the current period of renewed nuclear activities . </P> <P> Nuclear weapon warhead designs fall into various categories . </P>

When did the north korean nuclear program start