HOW DID IT COME TO THIS?
The latest crisis erupted when North Korea fired a long-range rocket on December 12 that splashed down near the Philippines. Pyongyang said it was a peaceful satellite launch and US experts acknowledge that the regime put a small object into orbit.
The United States and its allies said that the launch was aimed at developing ballistic missile capabilities and moved at the United Nations to tighten sanctions. North Korea voiced anger and carried out its third nuclear test on February 12, defying even its main ally China.
The UN Security Council on March 7 unanimously approved new sanctions that include greater scrutiny of shady financial dealings by the impoverished regime.
North Korea had warned of consequences for the UN vote and afterward renounced a 1953 armistice that ended the Korean War and declared itself at war with the US-allied South.
North Korea's military has said it has final approval for a nuclear strike on the United States.
WHAT DOES NORTH KOREA WANT?
Experts know little about North Korean leader Kim Jong-Un, who is believed to be in his late 20s and who succeeded his father Kim Jong-Il in December 2011.
North Korea has indicated that it wants recognition as a nuclear weapons state -- seen as a guarantor of the regime's survival. The United States has refused.
Some experts believe North Korea is operating from a playbook of steadily upping the ante and had planned out actions to coincide with the inauguration of conservative South Korean President Park Geun-Hye.
WHAT ROLE HAVE US-SOUTH KOREA EXERCISES PLAYED?
The United States and South Korea are carrying out their annual "Foal Eagle" exercises through April after starting them in March. North Korea regularly denounces the tests as a preparation for war, but tensions have been especially high this year.
The United States took the unprecedented step of announcing a test run by its nuclear-capable B-2 bombers. US officials said the step was meant to reassure South Korea, but Pyongyang voiced outrage and US peace activists called the move provocative.
The United States has also sent to South Korea its stealth F-22 jets, moved two destroyers to nearby waters and -- in response to North Korean threats against US bases -- sent a missile defense battery to its Pacific territory of Guam.
WHAT ARE NORTH KOREA'S CAPABILITIES?
North Korea is seen as capable of attacking South Korea and Japan, but experts doubt it can strike the United States with the possible exception of Guam.
The Arms Control Association research group estimates that North Korea's Rodong-1 missile has a range of 1,300 kilometers (800 miles). The Musadan theoretically has a range of 3,000-4,000 kilometers (1,900-2,500 miles), but North Korea has never tested it.
WHAT ARE THE US MILITARY RESOURCES IN THE REGION?
The United States stations 28,500 troops in South Korea and around 50,000 in Japan. It also keeps nearly 6,000 troops in Guam, a base for fighter-bombers and submarines, and 50,000 troops in Hawaii.
More than 40 US Navy vessels are permanently based in the Pacific with plans to increase the number as part of a growing US focus on Asia.
The Yokosuka base south of Tokyo is home to the USS George Washington aircraft carrier, two cruisers and seven destroyers. The USS John Stennis aircraft carrier is temporarily in Singapore on its way back from a mission in the Gulf.
ARE WE ON THE BRINK OF WAR?
Most experts consider North Korea's threats to be bluster but warn of the potential for miscalculations to blow up.
Stanford University's Siegfried Hecker, to whom North Korea revealed a uranium enrichment facility in 2010, doubted that Pyongyang would use nuclear weapons even if it could as such a step would "result in a devastating military response and would spell the end of the regime."
Still, North Korea has a history of taking action around April 15, the 101st birth anniversary of the regime's founder Kim Il-Sung, grandfather of Kim Jong-Un.