Earlier this month, China and North Korea hailed their 75 years of diplomatic relations by reaffirming ties that they once described as being close as “lips and teeth.”

       But North Korea’s decision to dispatch thousands of troops to Russia to fight Ukraine, revealed this week by Defense Secretary Lloyd J. Austin III, will test those bonds like never before.

       China has been frustrated by the instability Pyongyang sows in North Asia with its nuclear weapons program and its periodic threats to annihilate South Korea. Now North Korea is inflaming a war in Europe, which could deepen a broader confrontation over the global order that pits the United States and its allies against an axis of anti-Western powers led by China and Russia.

       China has tried to cast itself as a force for peace and contrast itself with the United States, which it accuses of trying to wage a new Cold War. The prospect of soldiers from China’s only treaty ally battling Western-backed forces on behalf of one of Beijing’s closest partners undermines that narrative.

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       Another concern China’s leadership may have, analysts said, is the exchange of military technology from Russia to North Korea in return for sending troops. That could embolden the North to act more aggressively toward South Korea or Japan, and at the same time, diminish Beijing’s ability to influence the reclusive state even as it relies on China for trade and aid.

       North Korea’s provocative behavior has already contributed to a trilateral security alliance between the United States, Japan and South Korea signed at Camp David last year. The pact, which China has likened to an Asian NATO, has added to Beijing’s feeling that it is being constrained and encircled by the United States and its allies.

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