SEOUL, South Korea (AP) — North Korean leader Kim Jong Un's surprise visit to China makes clear that Beijing, the North's only major ally and chief provider of energy and trade that keeps the country's broken economy afloat, will have a major role in any effort to rein in the North's nuclear program.

A look at key moments in relations between North Korea and China:

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October 1949: North Korea and China establish diplomatic relations.

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October 1950: China intervenes in the Korean War and engages in combat with U.S.-led forces, saving North Korea from defeat. The war ends in 1953 with an armistice.

November 1958: North Korea founder Kim Il Sung visits China, shortly after China withdraws troops from the Korean Peninsula. He successfully requests economic aid in meetings with Chinese leader Mao Zedong. Kim goes on to visit China and the former Soviet Union many times through the 1960s while maintaining a balancing act between the competing communist powers and consolidating his leadership at home.

April 1982: Chinese leader Deng Xiaoping visits North Korea to attend celebrations of Kim Il Sung's 70th birthday. Kim visits China five months later to discuss his plans to pass his leadership to his son, Kim Jong Il, and also reassure Beijing that the North wouldn't tilt toward the Soviet Union once he's no longer in power.

August 1992: China establishes diplomatic relations with South Korea, complicating its relations with the North.

May 2000: Kim Jong Il, who took power in 1994 after his father's death, makes the first of his eight visits to China as the North Korean leader. The trip was reportedly aimed at consulting with the Chinese leadership weeks before Kim's summit with then-South Korean President Kim Dae-jung, which opened a temporary era of rapprochement between the rivals. Kim, rumored to have had a fear of flying, traveled to China on a green-and-yellow armored train that was also used by his son this week.

August 2003: North Korea joins first round of six-nation nuclear talks in Beijing, which include China, Japan, Russia, South Korea and the United States. The talks continue periodically over the next several years before stalling.

December 2011: Kim Jong Un takes power after the death of his father.

May 2013: Senior North Korean official Choe Ryong Hae visits China as Kim's special envoy and meets with Chinese leader Xi Jinping.

October 2015: Senior Chinese official Liu Yunshan visits the North and attends a military parade with Kim.

March 2018: Kim visits Beijing for a meeting with Xi, weeks after the announcements of his planned summits with South Korean President Moon Jae-in and President Donald Trump.