Chinese President Xi Jinping has assured US President Donald Trump that China has limited influence over North Korea, but that's only half true.
It's true that diplomatic relations between the two are weak. Xi has never visited Kim Jong Un in Pyongyang, and Kim has never been to Beijing. High-ranking officials with ties to China in North Korea have been executed at Kim's order, sometimes with packs of dogs, sometimes with anti-aircraft guns.
But Gordon Chang, the author of "The Coming Collapse of China," writes in The Cipher Brief that 90% of North Korea's trade is done with China, accounting for 90% of its oil and, in some years, 100% of its aviation fuel.
After a provocative North Korean missile launch in 2003, China cut off its supply of oil to North Korea for three days. In no time, the Kim regime caved to international demands and sat down for the six-party talks on nuclear disarmament.
"China can disarm North Korea in the blink of an eye," Chang wrote.
And it could do so by crippling North Korea's economy - but at a huge cost to North Koreans.
Sanctions on North Korea do not affect regular trade. Although the UN takes very seriously the prospect of an aggressive, nuclear-armed North Korea, economic warfare in the form of too-harsh sanctions would harm or kill civilians - China also supplies at least a third of North Korea's food, according to Chang.
Additionally, China pressing North Korea to the point of regime collapse would contradict its interests, as Beijing doesn't want to face a strong, democratic, unified Korea on its border that could play host to US military installations.
