With a tweet in early January saying, "It won't happen!" Donald Trump, who had not yet been inaugurated president of the United States, set upon a confrontational course to stop North Korea from developing a nuclear-armed intercontinental ballistic missile capable of reaching the U.S.
During the presidential campaign, Trump unnerved allies in Asia with his "America First" threats to withdraw U.S. forces from South Korea and Japan unless they significantly increased defense-sharing payments, and his expressed willingness to negotiate with North Korean leader Kim Jong Un over hamburgers.
But after taking office Trump made ending the North Korean nuclear threat a top national security priority, and he embraced a "maximum pressure" strategy of imposing crippling sanctions on the Kim government, backed by the credible threat of military force.
"He has raised all kinds of expectations about what he's going to do about North Korea. And if he doesn't do those things, then it seriously threatens his identity, it undermines him, it undercuts him," said North Korea analyst John Delury with Yonsei University in Seoul.
Meeting with Japanese Prime Minster Shinzo Abe, Trump found strong support for his hard-line North Korea policy from a key Asian ally.
In February, U.S. Defense Secretary Jim Mattis traveled to Tokyo and Seoul to reaffirm the U.S. commitment to maintaining a strong military presence in the region, while downplaying the president's past criticisms of defense costs.
In April, on the same day Trump dined at his Florida Mar-a-Lago resort with Chinese President Xi Jinping, he ordered a unilateral missile strike on Syria for allegedly using chemical weapons against civilians.
Trump's demonstration of military force, his supporters said, sent a message to Xi that if China did not act to curtail North Korean provocations, the U.S. would.
Both Secretary of State Rex Tillerson and Vice President Mike Pence also went to the region, warning that the U.S. would not rule out preemptive military action to eliminate the growing North Korean nuclear threat to the U.S. mainland.
However, South Korea, after the impeachment of conservative President Park Geun-hye, elected the liberal Moon Jae-in, who strongly opposes the use of offensive military force on the Korean Peninsula.
"President Moon has been quite clear that he believes that war on the Korean Peninsula should never be considered an option, unless the North Koreans start it first, of course," said David Straub, a North Korea analyst with the Sejong Institute.
Moon, though, has also aligned closely with the U.S. on deterrence and sanctions as his efforts to reduce regional tensions through engagement and dialogue have been rejected by the North.
Proponents of military intervention, like Republican U.S. Senator Lindsey Graham of South Carolina, argue that it would be justifiable to use force to prevent a North Korean nuclear attack on the U.S. mainland. But even Mattis acknowledged a military conflict with North Korea would be "tragic on an unbelievable scale" and most likely trigger attacks against South Korea or Japan that could quickly escalate into widespread war.
During the year, Tillerson seemed to soften his hard-line position, moving to support unconditional talks with leaders in Pyongyang and dropping any demand that they first agree to give up their nuclear program.
"We have said, from the diplomatic side, we are ready to talk anytime North Korea would like to talk, and we are ready to have the first meeting without preconditions." Tillerson said in December.
But Trump has repeatedly rebuked his top diplomat, publicly tweeting in October that Tillerson was "wasting his time" trying to restart talks with North Korea.
Tillerson later clarified that North Korea must earn its way to the negotiations table by suspending further missile and nuclear tests.
Trump's critics have dubbed the mixed messages coming from the White House as a policy of "strategic confusion."
Undeterred by Washington's threats and increasing economic sanctions, Pyongyang continued to test ballistic missiles throughout the year, steadily improving their range and technical capability.
In February, the brutal nature of the repressive regime was again exposed when alleged North Korean agents using poison were charged with assassinating Kim Jong Nam, the half brother of leader Kim Jong Un, at the Kuala Lumpur airport in Malaysia.
And in June, Americans reacted with outrage when North Korea released American student Otto Warmbier in comatose state. Warmbier was arrested in 2016 for allegedly stealing a propaganda poster from his hotel and soon fell into a coma from which he never awoke. He died soon after returning home.
In response, Congress passed a bill banning most U.S. travel to North Korea.
War of words
In August, tensions escalated to the brink of conflict when Trump warned that North Korea would face "fire and fury" if it threatened the U.S. Pyongyang responded by saying it was considering test-firing an ICBM into waters near the U.S. Pacific territory of Guam.
Pyongyang would back down from this threat, but soon launched two long-range missiles over Japan, and in September it conducted its sixth nuclear test.
The U.S. and its allies did not respond with military strikes, but did persuade China and Russia to support stronger international sanctions that banned the North's lucrative coal and mineral exports and cut off one-third of oil imports.
Trump escalated a war of words with Kim during his address to the Untied Nations in September. The president referred to the North Korean leader as a "Rocket Man" on a suicide mission.
Kim responded in a statement calling Trump a "dotard" — an old person, especially one who might be weak or senile — and described his behavior as "mentally deranged."
After conducting a successful test in November of a long-range Hwasong-15 missile that has the potential to reach the U.S. mainland, North Korea announced it had reached its goal of developing operational ICBM capability. Some U.S. and South Korean experts said the North was still a year or so away from having an "operational" ICBM armed with a miniaturized nuclear weapon.
Few expect diplomatic breakthroughs anytime soon, but with South Korea hosting the upcoming Winter Olympics, there may be a new opportunity to reduce the potential for conflict in the region. Seoul is encouraging North Korea to participate in the Olympics, and there is talk that the U.S. and South Korea may postpone joint military exercises until after the games. These developments could bring a needed pause to the provocations.
Youmi Kim in Seoul contributed to this report.