China is North Korea's most important ally, biggest trading partner, and main source of food, arms, and fuel. China has helped sustain Kim Jong-Il's regime and opposed harsh international economic sanctions in the hope of avoiding regime collapse and an uncontrolled influx of refugees across its 800-mile border with North Korea. After Pyongyang tested a nuclear weapon in October 2006, experts say that China has reconsidered the nature of its alliance to include both pressure and inducements. North Korea's second nuclear test in May 2009 further complicated its relationship with China, which has played a central role in the Six-Party Talks, the multilateral framework aimed at denuclearizing North Korea. CFR's Scott Snyder and See-won Byun of the Asia Foundation argue the nuclear tests highlight the tensions (PDF) between China's "emerging role as a global actor with increasing international responsibilities and prestige and a commitment to North Korea as an ally with whom China shares longstanding historical and ideological ties." Beijing continues to have more leverage over Pyongyang than any other nation, say some analysts. The economic leverage in particular, some point out, has only grown as a result of North Korea's declining relations with South Korea and the international community. But most experts agree that Beijing is unlikely to exercise its leverage given its concerns regarding regional stability and the uncertainty surrounding regime succession in North Korea.
China has supported North Korea ever since Chinese fighters flooded onto the Korean peninsula to fight for their comrades in the Democratic People's Republic of Korea (DPRK) in 1950. Since the Korean War divided the peninsula between the North and South, China has lent political and economic backing to North Korea's leaders: Kim Il Sung and his son and successor, Kim Jong-Il.