President Donald Trump had ordered the U.S. military to evacuate the inhabitants of Seoul from the city in 2017 as well as 2018, according to a new book by CNN journalist Peter Bergen. This applied to all civilians of Seoul including South Korean citizens as well as families of the U.S. armed forces stationed in South Korea. This was around the time that the North Korea leader Kim Jong-un was frenziedly carrying out a spree of missile tests.

According to Bergen, Trump was shown in the Oval Office in 2017 a satellite image of the Korean peninsula at night, showing the lights of China and South Korea and the blackness of North Korea in between. Trump initially mistook the void for an ocean. When he was shown the bright lights of Seoul just 30 miles south of the demilitarized zone separating the two Koreas, the president asked: “Why is Seoul so close to the North Korean border?”

Trump had been told time that US freedom of action against North Korea was constrained by the fact that the regime’s artillery could decimate the South Korean capital in retaliation for any attack, inflicting mass casualties on its population of 25 million.

“They have to move,” Trump said, according to Bergen, who adds that his officials were initially unsure if the president was joking. But, Trump repeated the line. “They have to move!”

Trump’s order was ignored. Pentagon officials and top brass of U.S. military thought it would be unwise to follow Trump’s orders. The former Secretary of Defense James Mattis refused to carry out  many of Trump’s diktats. Mattis thought that evacuation of Seoul would be seen as an act of war by paranoid North Korea.

Although no action was taken in response to Trump’s bizarre remark, the situation grew steadily worse, with a series of North Korean intercontinental ballistic missile tests and a hydrogen bomb test in September 2017.

The noises made by both sides had reached a crescendo in the summer of 2017.

After watching retired four-star general Jack Keane saying in January 2018 on Fox News that U.S. troops deployed to South Korea must not take their families with them, Trump told his national security team: “I want an evacuation of American civilians from South Korea.”

A senior official on the team warned an evacuation would be seen by North Korea as a sign that the US was ready to go to war. Trump is reported to have ignored the warning. He  told his team: “Go do it!”

Shocked Pentagon officials again ignored the order. Trump eventually dropped the idea. It was one of several occasions where Mattis ignored directions from the White House.

Mattis also refused to send defense department officials to a planned Korea war game at Camp David in the autumn of 2017 or to provide military options for intercepting North Korean ships suspected of sanctions busting.

Bergen’s book is being published at a time when friction between Washington and Pyongyang is again on the rise, after more than 18 months of detente and summitry. The North Korean leadership is threatening a resumption of missile tests, and a war of words between Trump and Kim is simmering once more.