Although at the beginning North Korea joined the Nuclear Non-Proliferation Treaty, they withdrew from it on January 2003. It was a consequence of the United States accusation. The USA government claimed that North Korea was unofficially funding a program of uranium enrichment. Because of that, they cancelled the 1994 Agreed Framework treaty and cut off the energy assistance. Two years after withdrawing, the officials from North Korea claimed that they own operational nuclear arsenal. In spite of North Koreans assurances, the United States did not believe that North Korea really posses such weapons. As a result, the government of North Korea decided to conduct tests.
There were three tests that North Korea initially conducted. The first one, with the yield of less than a kiloton, took place in 2006. However, to show that this was in fact a nuclear detonation, North Koreans conducted second and third tests, respectable in 2009 and 2013. The maximum power of the blast of the aforementioned tests can be estimated to be up to 40 kilotons. However, a lot of sources claim that yield did not surpass 10-15 kilotons. Noteworthy is also the fact that in 2016, North Korea announced that they have conducted their first hydrogen-bomb test.