In North Korea's case, it was US President Donald Trump's now-infamous "fire and fury" ultimatum that kicked off the biggest tensions: "North Korea best not make any more threats to the United States. The problem is the jury's still out on whether Trump's North Korea strategy will ultimately bear fruit. Trump formally abandoned the Iran nuclear deal, to the dismay of both Iran and its European signatories in May, 2018. Washington worries this approach could be easily exploited by North Korea. And the US will likely only develop a normal relationship with North Korea if it abandons its nuclear weapons program.

Source: CNN May 21, 2019 03:00 UTC