When Kim Jong-Un came to power in North Korea in late 2011, some saw a young, untested leader destined for failure, while others detected a glimmer of reformist hope in the Swiss-educated heir to the ruling Kim dynasty.

One year, one successful long-range rocket launch and one nuclear test later, they have all been proved wrong.

Kim, believed to be in his late 20s, has prospered, consolidating his power base at home and showing the same disdain for global censure as his late father, Kim Jong-Il.

And early suggestions of a reformist bent that might signal a shift from the "Songun" ("Military First") policy of his father have come to nothing, as Tuesday's nuclear test emphatically underlined.

"Any hopes that the first year of the young dictator's reign would signal a departure from his father's hardline policies have been dashed," said Andrei Lankov, a North Korea expert at Seoul's Kookmin University.

"Kim has proved himself to be a loyal son, following in his father's footsteps, while at the same time delivering results his father could only dream about," Lankov said.

Kim's most visible successes came in quick succession, with the launch of a long-range rocket in December and then the nuclear test just two months later.

The first marked a significant step forward in North Korea's ballistic prowess, while the test was markedly more powerful than its predecessors in 2006 and 2009 and, according to Pyongyang, far more sophisticated.

"The test, coming on the back of the rocket launch, covers multiple bases for Kim Jong-Un," said Yoo Ho-Yeol, a North Korean expert at Korea University.

"As well as proving his loyalty to his father's legacy, he's demonstrated his leadership qualities and gained an upper hand in negotiations with other countries," Yoo said.

Most analysts stress that the "loyalty" issue was crucial given the dynastic nature of North Korea's leadership.

Kim Jong-Un's sole priority, they argue, was to cement his legitimacy as the dynastic successor and demonstrate his loyalty to the legacies of his father and grandfather, the North's founding leader Kim Il-Sung.

While Kim's more open, smiling style might contrast with his father, the outward policy stance of belligerent intransigence was unchanged.

"One of the things we have to realise is that even though it's a different leader, the policies seem more or less the same -- the use of threats, intimidation and provocative behaviour to a particular end," said Philip Yun, executive director of the US-based Ploughshares Fund.

North Korea's internal politics are so opaque that there will always be questions about where the real decision-making power in the leadership resides, and whether Kim's role extends beyond that of symbolic figurehead.

The state propaganda machine has certainly pushed him as an active leader, providing prominent coverage of his meetings with top security officials prior to Tuesday's nuclear test.

And under Kim's watch, the North's missile and nuclear programmes have made highly-visible strides in a very short period of time.

The response of the international community, particularly the United States, has been to warn North Korea that it faces further isolation.

But Kim's leadership has shown no outward sign of concern at the prospect, not even when sole ally China has hinted at a reduction in crucial economic aid.

"Since coming to power, Kim has shown a distinct willingness to violate previous agreements, provoke the international community, and crack down harshly at home to preserve his power," said Nicholas Hamisevicz at the Korea Economic Institute of America.

"The time has come to abandon any lingering illusions about the nature of Pyongyang's leadership and prepare for a period of tension and provocation," Hamisevicz said.