Before today,... North Korea had conducted four nuclear tests in the space of around a decade. For a summary of the timeline of the previous tests,... Oh Soo-young reports. Nuclear tests have been North Korea's go-to last resort when backed into a corner. Pyongyang's first test came on October 9th, 2006 in protest of the U.S. freezing North Korean assets held in a Macau-based bank. The U.S. Geological Service's detection of a four-point-three magnitude tremor at the Punggye-ri nuclear test site signaled North Korea's arrival as the world's eighth nuclear power. On May 25th, 2009 less than a month after North Korea walked away from the six-party nuclear talks aimed at its denuclearization, Pyongyang conducted a second underground test claiming that it had detonated a plutonium device. A four-point-seven magnitude earthquake was detected at Punggye-ri with an estimated yield of three to four kilotons, a significant jump from an estimated explosive force of less than one kiloton in 2006. The regime's third nuclear test was conducted on February 12th, 2013, with the North claiming to have tested a "miniaturized and lighter nuclear device with greater explosive force". The speculation was that North Korea used uranium, marking a major leap forward from the plutonium bombs used in its previous two tests. It was also the first test under the new and young leader Kim Jong-un and came when talks with Seoul and Washington stalled.