https://www.wsj.com/articles/north-koreas-missiles-and-nuclear-weapons-everything-you-need-to-know-11610712018?mod=world_major_1_pos1
North Korea sees its nuclear program as essential to regime survival, serving to deter a U.S.-led invasion. Decades of denuclearization talks, economic sanctions and diplomacy have done little to slow Pyongyang’s advance to becoming a self-declared nuclear state.
One of the world’s poorest and most-isolated countries, North Korea has managed to stay high on Washington’s list of foreign-policy priorities for years. It spends more on its military, as a ratio of gross domestic product, than any other of the 170 countries tracked by the U.S. State Department.
Pyongyang developed its weapons program brazenly, flouting sanctions and breaking promises to halt nuclear production. In 2003 it withdrew from the Nuclear Non-Proliferation Treaty, the main global commitment to stopping the spread of nuclear weapons.
At 2018’s Singapore summit with President Trump, Kim Jong Un greatly boosted his global legitimacy by becoming the first North Korean leader to meet a sitting U.S. leader. In 2017 Pyongyang had ratcheted up tensions with the U.S. to their highest level in years by conducting its sixth nuclear test and firing off three intercontinental ballistic missiles—the last of them showing the range to strike anywhere in the U.S.