It rarely happens that one country’s actions unite the world in condemnation, yet this is what North Korea has achieved with reports of its latest underground nuclear test explosion. But this act of universal defiance has also underscored the long-running failure of the international community to rein in Kim Jong-un, North Korea’s youthful dictator, and the country’s dangerous military regime.

Impassioned denunciations of Pyongyang’s new year surprise rang out across the globe, from Washington and Brussels to Tokyo and Canberra. Russia, typically, warned that the test, the country’s fourth, would aggravate tensions and increase “the high potential for military and political confrontation” on the Korean peninsula.

But it was the reaction of China – ostensibly North Korea’s only friend – that was most significant. Beijing formally protested, expressed concern over radioactive fallout in areas bordering North Korea, and indicated it would support new, punitive UN security council action as demanded by South Korea, among others.

Maybe Beijing’s undisguised wrath will give Kim pause. But maybe not. In a deliberate poke in the eye for China’s leaders, he failed to inform them of the test in advance. Kim has refused to rejoin the Chinese-led six-party nuclear talks. In September, he snubbed an invitation by China’s president, Xi Jinping, to attend celebrations marking the end of the second world war. In fact, Kim has never visited his Chinese ally.

A visit to Pyongyang last October by Liu Yunshan, a senior Chinese party official, suggested relations were warming up. Now Kim has slammed the door again. In truth, China has less leverage over Pyongyang, both politically and in terms of trade and oil supplies, than is commonly believed. So perhaps the boyish Kim, the self-styled supreme leader, does not really care what “Big Daddy” Xi wants.

Or perhaps, more alarmingly, Kim does not know what he is doing.

Conventional diplomatic wisdom suggests China will not break with North Korea’s regime for fear of internal collapse, a refugee crisis, and a US-South Korean takeover. But there is more than one way to skin a cat. Tough bilateral Chinese sanctions in addition to UN measures are one option, plus a halt to Chinese aid, investment and joint projects.

If China does not act, it is unclear who will. Washington’s carrot-and-stick policy of alternate engagement and ostracism, dating back to the Clinton administration, has patently not worked. What is clear is the dictatorship has grown steadily more vicious and threatening since Kim took power in 2011, succeeding his late father, Kim Jong-il.

Inexperienced – he will by 33 on 8 January – and fearing for his position, Kim ruthlessly purged possible opponents in Stalinist fashion while extending his grip on the all-powerful military. In one chilling episode in 2013, he disgraced and executed his uncle and former mentor, Jang Sung-taek, plus all of Jang’s relatives, children and grandchildren.

Systemic, gross human rights abuses, including forced labour camps and executions, have reportedly worsened under his rule, leading a UN commission to demand Kim be investigated for crimes against humanity.

In his 2013 new year’s address, Kim imposed martial law amid reports that 10,000 people died in a famine in north and south Hwanghae provinces. He also ordered the country’s third nuclear test, which led directly to additional UN sanctions. Undeterred, Kim provoked another crisis last summer along the border with South Korea, placing his army on a war footing after the two sides exchanged artillery fire.

Colourful reports persist, meanwhile, about his eccentric personal lifestyle, his fondness for partying and alcohol, and an apparent obsession, shared with his elder brother, Kim Jong-chol, with western icons such as the American basketball player Michael Jordan and the British rock star Eric Clapton.

Kim’s latest exploit will confirm his reputation as a dangerous maverick and international outlaw. Why he pressed the button now is unclear. It could be attention-seeking, or the prelude to a new offer of normalisation talks, arising from domestic weakness. It could be that he wants to demonstrate his control, linked to the suspicious death, allegedly in a random road accident, of another top adviser, Kim Yang-gon.

Or perhaps detonating a nuclear device is simply Kim’s idea of a fun birthday. Dr Strangelove would have understood.