China is North Korea’s most important ally, biggest trading partner, and main source of food, arms, and energy. The country has helped sustain what is now Kim Jong-un’s regime, and has historically opposed harsh international sanctions on North Korea in the hope of avoiding regime collapse and a refugee influx across their border. But after Pyongyang’s third nuclear test in February 2013, analysts say that China’s patience with its ally may be wearing thin. This latest nuclear test, following previous ones in 2006 and 2009, has complicated North Korea’s relationship with Beijing, which has played a central role in the Six Party Talks, the multilateral framework aimed at denuclearizing North Korea. The December 2013 execution of Jang Song-taek, Kim Jong-un’s uncle and adviser with close ties to Beijing, spurred renewed concern from China about the stability and direction of the North Korean leadership. Furthermore, experts say that thawing relations between China and South Korea could shift the geopolitical dynamic in East Asia and undermine the China-North Korea alliance.