Barack Obama
Neither Carrot Nor Stick
Just month’s into President Barack Obama’s first term, the North detonated a series of nuclear bombs.

Rather than negotiate, Mr. Obama imposed a policy of “strategic patience,” hoping that through sanctions and espionage, the United States could wait out the isolated state.

Mr. Obama hoped that the North would eventually feel it had reason to negotiate and make a good-faith effort at talks. Instead the North pursued its weapons program and launched a series of cyberattacks on American businesses, including Sony Pictures.

Mr. Obama also talked tough with the North Koreans when he thought it necessary: In 2014, he warned that the United States “will not hesitate to use our military might” to protect American allies.

North Korea’s Response
It was during the Obama administration that Kim Jong-un, a grandson of the country’s founder, was named leader after the death of his father, Kim Jong-il. The youngest Mr. Kim quickly eliminated those who might challenge his leadership and began a program, using new technology, to develop an intercontinental missile.

The Americans initially hoped the young leader would represent a break from the hard-line policies of his predecessors, but instead he doubled down. In September 2016, he tested a nuclear warhead that he claimed could fit on a long-range missile.