This article first appeared in Caixin.

BEIJING - China has always been clear about its "firm opposition" to North Korea's development of a nuclear weapons program. But as the international community's negotiation over the issue has stalled, Pyongyang continues to develop its nuclear technology. It is a provocation that leaves China little room for diplomatic maneuver.

China has carried out a notable strategic readjustment on this matter in recent days, led by Chinese Foreign Minister Wang Yi citing three non-negotiables vis-à-vis North Korea, and working with the Americans to push through a new United Nations Security Council resolution on sanctions.

The unanimous approval by the UN Security Council on March 2 included unprecedented sanctions in the fields of finance, trade and technology to punish North Korea for its recent nuclear testing. The UN resolution also stresses that if Pyongyang conducts any more atomic tests or ballistic missile launches, it will "take further significant measures."

This Sino-American approach came after years of Beijing and Washington failing to agree on how North Korea should be sanctioned. The result reflects how the interests the two countries share on this issue are critical to both. As U.S. Undersecretary of State for Political Affairs Wendy R. Sherman told this newspaper in January 2015, if China makes it clear that North Korea's abandoning its nuclear program is its top priority, this will be of great help in solving the problem.

Foreign Minister Wang Yi recently specified China's three key points in how it will handle its policy on the Korean Peninsula: First comes the denuclearization of the peninsula, whether in the south or the north, and whether self-made or introduced deployment; second, there is no solving the problem by force, because this will lead to war and chaos, which China cannot allow; third, China's own legitimate national security interests must be effectively maintained and protected.

In a Feb. 25 speech given to an American think tank, the Center for Strategic and International Studies, Wang Yi acknowledged that the UN resolution is bound to affect the relationship between Beijing and Pyongyang, but is necessary in order to achieve the denuclearization of the peninsula. This is sending a strong message to North Korea: Denuclearization cannot be challenged.

As North Korea's biggest neighbor, one with historical ties, and as the world's second largest economy and a permanent member of the UN Security Council, China indeed should assume its responsibility on the North Korean nuclear issue.

Blood brothers

Another key difference with past Pyongyang provocations is that this time, with more online communication, North Korean actions have aroused a lot more discussion among the Chinese public. The seismic effects triggered by the nuclear test, the cracking of a school playground, as well as the pollution the test may have caused along the Chinese border, are all causing an unprecedented questioning of the Sino-North Korean relationship among Chinese.

China used to call its relation with North Korea a "friendship sealed in blood." But this bilateral relationship had already undergone a major shift in 1992, when China established diplomatic relations with South Korea. Meanwhile as Beijing normalizes relations with countries with different ideologies and political systems, and moves towards the center of the international stage, it has inevitably drifted further away from its historical alliance with North Korea.

Over the past two decades, every time North Korea conducted a nuclear test or a ballistic launch, the two countries' relations deteriorated. In the era of Kim Jong-il, such new lows didn't have much impact, and both sides' leaders regularly visited each other. However since his son, Kim Jong-un, has come to power, the high-level exchanges between the two have been reduced significantly.

The cooling of relations between Beijing and Pyongyang is also linked to a huge gap in social development in the two countries. China continues to move forward, assuming an expanding international role in correspondence with its strength, while North Korea stands still and adheres to "military first" Songun politics regardless of its people's livelihood. If some from the older generation of Chinese still feel sentimentally attached to the ties between the two states during the Korean War, the young generation of Chinese are much more pragmatic, and find it difficult to identify with a North Korea they see as both foolish and offensive.

Sino-North Korean relations have come to a point where they must adapt to the realities of both the international system and public opinion. Though China's support for the UN sanctions resolution was a good start, it must now show Pyongyang that it is determined to follow through. After all, the first victim of North Korean instability is China.