The Yalu River running through Manchuria has long served as the well-known border between China and North Korea. What is less known, but equally significant, is the short, aging 30 km Friendship Pipeline constructed in part under the Yalu. The pipeline, vital to North Korea's economy, transports over 500,000 tons of oil annually to the Ponghwa refinery near Sinuiju, where diesel and gasoline are manufactured. Without the pipeline North Korea's economy would collapse and this is why it is seen in the West as lever to increase the pressure on Pyongyang to back away from its nuclear weapons program.

This would be an exercise in soft power, the preferred option of the majority members of the UN Security Council, one with real teeth. But up to now the Chinese are loathe to wield this ultimate soft power tool.

Their reasons are not just political: China National Petroleum Corporation has said that stopping the flow of oil through the Friendship Pipeline might damage the pipeline. In 2011, engineers for the company wrote that wax in the crude oil could build up and block the pipe if the flow were stopped. They said it was safe to stop the flow for eight hours at most during summer, and for no more than two hours during winter.

In other words stopping the flow of oil might permanently damage the pipeline. And the Chinese fear that this would not only trigger an economic collapse but a mass movement of North Koreans seeking refuge in China. It has been reported that the Chinese are already preparing for such an event by erecting refugee camps on its side of the border.

Given conciliatory talks between the two Koreas this week it would seem that the Friendship Pipeline will continue to operate, upholding neighborly relations, as its name implies. Yet with President Donald Trump's saber-rattling on the one side and Kimm Jong Un's on the other, this could quickly change in the charged geopolitical environment.