When President Trump was inaugurated, relations with North Korea were at a very low point. North Korean dictator Kim Jong Un thought he could bully the US and gain concessions, as he and his predecessors had in the past.
President Trump responded to Kim’s bluster in usual Trump fashion–he gave him the nickname “Little Rocket Man”. 
He made it very clear the United States under President Trump would not be intimidated by the North Korean despot.
Even before his inauguration, Trump tweeted on January 2, 2017 “North Korea just stated that it is in the final stages of developing a nuclear weapon capable of reaching parts of the U.S. It won’t happen!”
During a lunch with ambassadors representing the member countries of the United Nations Security Council on April 24, Trump touched on how the group’s policy toward North Korea needs to change.
“The status quo in North Korea is also unacceptable, and the council must be prepared to impose additional and stronger sanctions on North Korean nuclear and ballistic missile programs. This is a real threat to the world, whether we want to talk about it or not. North Korea is a big world problem, and it’s a problem we have to finally solve. People have put blindfolds on for decades, and now it’s time to solve the problem,” he said.
During a June 30, 2017 press conference at the White House with South Korea’s President Moon Jae-in, Trump said, “The years of strategic patience with the North Korean regime has failed. Many years and they failed. It’s failed. And frankly, that patience is over.”
“Together we are facing the threat of the reckless and brutal regime in North Korea. The nuclear and ballistic missile programs of that regime require a determined response. The North Korean dictatorship has no regard for the safety and security of its people or its neighbors and has no respect for human life. And that’s been proven over and over again,” he said.
North Korea fired an ICBM on July 4, 2017. On August 5, the U.N. Security Council unanimously approved sanctions to penalize the regime for its escalating nuclear program and missile launches. North Korea responded two days later, claiming that it would take “thousands-fold” revenge against the United States in response to the latest round of international sanctions over its nuclear program.
On August 8, President Trump stated, “North Korea best not make any more threats to the United States. They will be met with fire and fury like the world has never seen. He has been very threatening — beyond a normal statement — and as I said, they will be met with fire, fury and, frankly, power the likes of which the world has never seen before,” Trump said, referring to North Korea’s statement about taking revenge. The next day, North Korea threatened the U.S. territory of Guam with “enveloping fire”.
In his first address to the United Nations on September 19, Trump chose not to use the North Korean dictator’s name, instead addressing him as “Rocket Man”. (This address was noteworthy, as it further solidified Trump’s ‘America First’ attitude. More information here.)
“I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man…Save your energy Rex, we’ll do what has to be done!” Trump wrote in two tweets on October 1. “Being nice to Rocket Man hasn’t worked in 25 years, why would it work now? Clinton failed, Bush failed, and Obama failed. I won’t fail,” he wrote in a later tweet that day. Click here for a history of US/NK relations from the Clinton through Obama eras.
Trump made a multi-stop, two-week visit to Asia and on November 7 during his visit to South Korea, he addressed the country’s National Assembly. “I hope I speak not only for our countries but for all civilized nations when I say to the North, do not underestimate us and do not try us,” Trump said. “All responsible nations must join forces to isolate the brutal regime of North Korea — to deny it any form of support, supply or acceptance,” Trump said. “The longer we wait, the greater the danger grows, and the fewer the options become.”
North Korea later responded to Trump’s speech, saying the speech was made up of “reckless remarks by an old lunatic.” And Trump responded with a tweet, writing, “Why would Kim Jong-un insult me by calling me ‘old,’ when I would NEVER call him ‘short and fat?’ Oh well, I try so hard to be his friend – and maybe someday that will happen!”
On November 28, 2017, North Korea launched an ICBM that is thought possibly capable of striking anywhere in the United States. North Korea called it a Hwasong-15 missile. Its potential range appears to be more than 8,000 miles, able to reach Washington and the rest of the continental United States. The regime has not made another missile or nuclear bomb test since.
Trump had sent a tweet that morning that said, “Sanctions and “other” pressures are beginning to have a big impact on North Korea. Soldiers are dangerously fleeing to South Korea. Rocket man now wants to talk to South Korea for first time. Perhaps that is good news, perhaps not – we will see!”
North Korea came up in Trump’s first State of the Union address on January 30, 2018, warning that the country’s “reckless pursuit of nuclear missiles could very soon threaten our homeland. We need only look at the depraved character of the North Korean regime to understand the nature of the nuclear threat it could pose to America and our allies,” Trump said in the speech.
The parents of American student Otto Warmbier, who died shortly after being returned to the U.S. from North Korean captivity, attended as special guests of the White House, as was Ji Seong-ho, a man who escaped hardship and torture in North Korea as a boy.
After all of the tough rhetoric from Trump and the frightening brinkmanship of Kim, what came next surprised almost everyone.