Pressures coming from external sources, such as the United Nations Security Council (UNSC) presidential statement along with additional pressures were combined with North Korea’s internal logic, which required it to conduct the second nuclear test as a nuclear power in response to changing international circumstances. Firstly, North Korea maintains the position that it has the status of a nuclear power. Secondly, since the basic principle of the Six-Party Talks, specifically sovereign rights, was denied by the UNSC presidential statement, North Korea thought that it was no longer bound by the agreement in the Six-Party Talks which required North Korea to abandon its nuclear program. Thirdly, the second nuclear test may be rationalized from a military viewpoint because North Korea saw another nuclear test as necessary in order to develop more elaborated nuclear warheads beyond the capabilities achieved following the first nuclear test in October 2006. Therefore, the UNSC presidential statement functioned as the trigger for North Korea to conduct the second nuclear tests at an “appropriate” time. This article uses the Neoclassical Realism perspective to explain why North Korea conducted its second nuclear test.