Welcome to a more dangerous world.
Welcome to a world where there is now, unquestionably, a new nuclear power.
Welcome to a world where the two great global powers are both threatened, in different ways, by a state that says it will never back down.
This world has been brought to you by North Korea, which has just passed a point of nuclear no return and thrown out a number of challenges.
First, in detonating a small, light nuclear weapon just weeks after proving it could launch a long range missile, it has joined the two pieces of the atomic weapon puzzle and made the final, major technological leap to becoming a nuclear power.
The United States must now consider its national security is threatened. North Korea could launch a nuclear missile and have some confidence that it could reach the West coast of America. That does not mean it has any intention of doing so. But the apparent capability is new. And dangerous.
Secondly, there is evidence that this test and December's launch of a rocket that might carry a nuclear warhead across the Pacific, was a product largely of North Korea's own scientists, with little or no new help from outside. There has been evidence in previous decades of help from Pakistan and Iran.
Thirdly, Intelligence agencies around the world will be looking at this test very closely. There is concern that what made the latest weapon so explosive was not Plutonium, which North Korea has in small supply, but Uranium.
If that's true and the state can manufacture this in highly enriched batches, then this presents the world with an even bigger headache. North Korea's capability might not stop at the five to ten Plutonium based devices its current stocks imply.
Welcome too, to a world where diplomacy has failed.
In recent weeks the world warned North Korea not to test this device. It ignored that.
Years of sanctions have failed to deter it.
But most of all, the diplomatic failure that began with George Bush labelling North Korea part of an "axis of evil" in 2002, has continued through six years of failed talks, ending in 2009, until this moment of nuclear explosion and a torrent of threats and boasts from North Korea's leaders.
So what do they want?
Not to be ignored, taken for granted, disrespected or replaced.
Oddly, although they consider the US their greatest enemy, they have always craved America's respect.
But negotiate about what?
North Korea says its nuclear capability is now non-negotiable. In fact, nuclear weapons are now the only bargaining chip the state has and it will continue to test them.
So what does it want?
It wants all international sanctions lifted.
And, in truth, these have failed, even though the world may be about to embark on new ones to punish North Korea.
It wants guarantees from the United States that there will be no attempt to remove its regime or attack it in a resumption of the unfinished Korean war.
In other words it wants what every country does; security, prosperity and peace.
It is not impossible it might agree, at some far distant talks, to freeze its nuclear programme in return for all of the above. But do not hold your breath.
It is choosing a strange way to get what it wants but secretive North Korea has always been an enigma.
So, the world has some big choices to make in the coming weeks and months.
After all the condemnation of the Koreans' "provocative" and "destabilising" act, will it impose more UN sanctions, in the belief that these will hurt the regime, and not the suffering millions of ordinary North Koreans?
Will China finally call its troublesome neighbour to order, reading the nuclear riot act, but promising it good times ahead if it desists from further tests or development?
And what will America do? President Obama is sure to be adding new lines to his State of the Union speech tonight.
But rhetoric won't replace clever policy. And so far, the US does not have one.
Perhaps all the world can do now is to minimise the damage.
The genie is out of the bottle. North Korea's new young leader is celebrating. But tensions are rising in East Asia. And the world is a more nervous place.