Photo: China and North Korea had a close relationship during the time of Mao Zedong and Kim-Il Sung. (Getty Images: VCG)
As North Korea edges closer to launching a nuclear weapon across the Pacific, President Donald Trump is demanding China pressure Pyongyang to stop its weapons program.But just how much influence does China have on North Korea? A look at the countries' recent histories shows the relationship is more complex than it may first appear.
Historically, China and the Korean peninsula have been extremely close. Prior to the first Sino-Japanese War in 1894, Korea was a tributary state of the Qing dynasty, which enjoyed substantial influence over Korea's Joseun court.
Even after becoming an independent state, Korea maintained tight relationships with China at "almost at all levels", according to Chung Min Lee, professor of international relations at Seoul's Yonsei University.
And since independence, the countries have also shared military ties: like many others of his time, Kim Il-sung, the first leader of North Korea, fought with the People's Liberation Army in China during the Second World War.
Relationships during the Korean WarUpon China's victory in 1945, many Koreans continued to support the Chinese Communist Party in the Chinese Civil War.
Then on June 25, 1950, North Korea launched an attack across the 38th parallel, marking the start of the Korean War.
According to James Reilly, an associate professor in North East Asian politics at the University of Sydney, this was "a crucial moment in the history of the People's Republic of China".
As a nation, China was just one year old — and Mao Zedong feared that if the Americans unified the Korean peninsula, his burgeoning nation would have a hostile neighbour.
The slogan in China at the time, Professor Reilly says, was to save Korea and resist America. "It was very much a moment of great pride for Chinese leadership, and for many Chinese people," he says.
After three years of fighting and millions of casualties, an armistice was signed between North Korea, China, and the United States.
Nuclear tensions begin to simmerEstimates vary as to the exact starting point for the North Korean nuclear program, but the establishment of Yongbyon Nuclear Scientific Research Centre in 1962 was a key moment.
For Xiao Ren, the director of the Centre for the Study of Chinese Foreign Policy at Fudan University, North Korea established the program primarily to safeguard its security.
"[The North Koreans] feel threatened by the United States — I believe that has been the most important reason for them to develop nuclear weapons," he says.
Professor Ren says that while China and North Korea were close allies during the Cold War years, today the alliance is more nominal.
The official position held by the Chinese government is to oppose North Korea's pursuit of nuclear weapons.
"They [have] signed onto every UN resolution … opposing North Korea's pursuit of nuclear weapons," Professor Reilly says.
Until recently, however, China had limited its sanctions to materials and individuals connected with the production of North Korean nuclear weapons — and resisted wider sanctions.
Professor Ren says China has taken major steps this year. "In February, China announced that it would stop [the importation] of coal from North Korea — which was a significant step, because it will reduce North Korea's foreign exchange income."
For many years, Professor Ren says, China tried to persuade Pyongyang that a nuclear program was not in North Korea's best interest.
But for the North Koreans, he says, "the top priority has been regime survival".
Where to from here?For decades, US policy has been predicated on the idea that the North Korean regime is about to collapse. But Professor Reilly says that, on the balance of historical evidence, it's a shaky assumption.
"North Korea survived its last leadership transition much more impressively than almost all the external US experts would have predicted," he says.
Professor Ren believes the possibility of a regime collapse is exactly why China is in a difficult situation.
"If North Korea collapses, it would have serious ramifications for China: the flooding of North Korean refugees, they have nuclear bombs, they have missiles, they have artillery and so on," he says.
"It would be very uncertain and risky if North Korea collapses. So China does not hope to see a collapse of North Korea."This attitude, Professor Ren says, is at odds with China's interest in regional non-proliferation. "We must find a middle way, right? But it's very difficult to balance between the different scenarios. China is in a very difficult situation."
For his part, Professor Reilly fears any military response to North Korea would be a disaster.
"It's extremely difficult to control the subsequent dynamics. The US should not be under any illusion about the depth of Chinese concerns on the Korean peninsula."