North Korea has been restive this year, picking up the pace of its missile and nuclear tests, a worrying development from a country that regularly threatens to turn South Korea into a "sea of fire."
Some analysts believe the country may be capable of hitting its neighbors with nuclear-tipped missiles by as early as 2020.
On January 6 of this year, the North conducted its fourth nuclear test, spurring a magnitude 5.1 earthquake. North Korea claimed it was a successful test of a hydrogen bomb, calling it a "H-bomb of justice."
"It was confirmed that the H-bomb test conducted in a safe and perfect manner had no adverse impact on the ecological environment," the official Korean Central News Agency (KCNA) of DPRK said at the time.
"This test is a measure for self-defense the DPRK has taken to firmly protect the sovereignty of the country and the vital right of the nation from the ever-growing nuclear threat and blackmail by the U.S.-led hostile forces," it said, calling the U.S. a "gang of cruel robbers" that had caused North Korea "thrice-cursed and unheard-of political isolation."
Outside experts were skeptical of the North's claim to possess an H-bomb, but the nuclear test spurred tough new United Nations sanctions on the country.
On February 7, North Korea fired a long-range rocket that it claimed put a satellite into orbit. At the time, the U.S. Strategic Command said it had detected a missile entering space, while South Korea's military said an object had been placed into orbit, Reuters reported. The object was believed to have at times achieved a stable orbit, but not to have transmitted data. But concerns were primarily that North Korea was using the launch as a cover to test a long-range missile.
On July 6, the U.S. placed North Korea's leader Kim Jong Un and other officials on a sanctions blacklist for the first time, citing a laundry list of human rights abuses. That meant those officials' assets would be frozen and they were barred from undertaking transactions with U.S. citizens.