By Timothy W. Martin 

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.

What are North Korea's nuclear capabilities?

The U.S. Army in July said North Korea may now have 20 to 60 nuclear bombs and the ability to manufacture six new bombs each year. In October, then-U.S. Defense Secretary Mark Esper said North Korea's nuclear and ballistic-missile programs remain "a serious threat to the security and stability of the region and the world."

Pyongyang has yet to show it can reliably strike the U.S. with a nuclear weapon. That requires developing a warhead that can survive the enormous pressure and heat of re-entering the atmosphere. And in its tests the North has launched ICBMs at a steep angle--in part to keep them from splashing down in U.S. territorial waters--which leaves doubts about whether the technology could traverse an actual flight, with its flatter trajectory.

Nuclear talks have stalled between Washington and Pyongyang, despite three meetings between Messrs. Trump and Kim. The two sides remain far apart on when and how the North should relinquish its nuclear arsenal. The last formal talks, in October 2019 in Stockholm, broke down after a single day. In a statement addressing U.S. affairs, Kim Yo Jong, the leader's younger sister, said denuclearization didn't seem possible at the moment.

What type of missiles does North Korea have?

Mr. Kim, in a policy speech published Jan. 1, 2020, declared he no longer felt bound by a moratorium on long-range weapons tests dating to late 2017. At an October military parade, the North showcased a new ICBM that weapons experts believe is the largest of its kind and could hold multiple warheads. Mr. Kim has recently said such technology is at a final stage of development.

Since the 2019 Vietnam summit ended without a deal, North Korea has conducted more than a dozen tests of shorter-range weapons that can't reach the U.S. mainland but endanger allies and overseas troops in South Korea and Japan. It has honed new launch systems, flown weapons designed to evade U.S. missile defenses and upgraded its submarine-fired technology.

When was the last time North Korea fired missiles?

Pyongyang conduced its last nuclear and ICBM tests in the fall of 2017. The nuclear test, in September, produced an estimated yield as high as 100 kilotons, according to a South Korean lawmaker--or roughly five times that of the atomic bomb the U.S. dropped on Nagasaki, Japan, in 1945.

The ICBM test came that November. The missile, dubbed the Hwasong-15, soared to an altitude of around 2,800 miles, or about 11 times as high as the International Space Station.

Mr. Kim accelerated the country's weapons development. In the three years before the Singapore summit in 2018, North Korea unleashed more major missiles than in the three previous decades. Of the country's 103 missile launches and nuclear tests, 72 have been conducted since Mr. Kim took power in late 2011, according to the Center for Strategic and International Studies, a Washington-based think tank with a database going back to 1984.

Can North Korea's missiles reach the continental U.S.?

The Hwasong-15 missile could potentially strike anywhere in the U.S., according to an assessment by the U.S. Forces Korea, which oversees the roughly 28,500 American personnel in South Korea.

Missile experts estimate its range at 8,100 miles, and say a North Korean ICBM could hit the U.S. mainland less than 30 minutes after launch.

In January, Mr. Kim outlined a goal of extending the flight range to about 9,300 miles.

The shorter- and medium-range weapons have repeatedly shown the North has ample ability to hit South Korea and Japan.

What has the U.S. response been to North Korea's missile tests?

Washington and Pyongyang have held denuclearization talks since President George H.W. Bush was in the White House and North Korea was still led by founder Kim Il Sung, Kim Jong Un's grandfather. Prior deals sought to freeze production, allow on-site inspections or dismantle facilities in return for aid or other resources. But the arrangements broke down after the North refused to comply or engaged in a military provocation.

Mr. Trump took a different approach, shifting negotiations customarily left to working-level officials to leader-level diplomacy. The Trump administration played down North Korean's resumption of weapons tests in spring 2019, because they didn't include ICBMs or nuclear bombs. The absence of long-range tests, Mr. Trump and senior officials said, was a sign the U.S. approach was successful. Others, like former U.S. national security adviser John Bolton, said the tests violated United Nations restrictions.

As recently as December 2020, Stephen Biegun, the U.S. special representative for North Korea, said Washington remained ready to resume nuclear talks with Pyongyang.

Without a nuclear deal that eases sanctions--which limit the North's access to foreign banks and global trade--Mr. Kim can't deliver on his promise to revitalize a North Korean economy that has crumbled during the pandemic. Living conditions have slid so much that Mr. Kim has apologized a number of times for the policy failure, a gesture previously unheard of in North Korea.

What is President-elect

Joe Biden

's stance on North Korea?

Mr. Biden has advocated mixing pressure with what he calls principled diplomacy. He has declared an end to holding summits without preconditions, which he said amounts to embracing a thug. Mr. Biden said he would sit down with Mr. Kim only if Pyongyang were sincere and pledged to reduce its nuclear arsenal.

North Korea hasn't acknowledged Mr. Biden's election victory. This month Mr. Kim called the U.S. his country's biggest enemy. North Korean state media last mentioned Mr. Biden by name in 2019, when it called him a "fool of low I.Q." and compared him to a rabid dog that "must be beaten to death."

Write to Timothy W. Martin at timothy.martin@wsj.com

(END) Dow Jones Newswires

January 15, 2021 07:14 ET (12:14 GMT)

Copyright (c) 2021 Dow Jones & Company, Inc.