By Gordon Corera
BBC security correspondent
The announcement of a deal over the North Korean nuclear programme represents a significant step forward, but it would be very surprising if the path ahead was smooth.
North Korean openness about its nuclear facilities is key to the deal
A number of serious obstacles lie in the way as well as a great deal of mistrust on both sides.
The last major deal over North Korea's nuclear ambitions was the Agreed Framework negotiated in 1994.
This froze Pyongyang's nuclear programme in return for light-water nuclear reactors and other assistance.
But one of the chief negotiators, Robert Gallucci, remembers coming back to Washington to brief the US Congress and being asked by congressmen if Pyongyang might cheat on the deal - he answered yes, they could.
And that is exactly what the US believed happened.
Soon after the plutonium facilities were frozen, the North Koreans began secretly receiving uranium enrichment technology from the Pakistani scientist AQ Khan (who also passed the technology to Iran and which is the basis of their Natanz facility).
In late 2002, the US confronted the North Koreans about the enrichment programme and the Agreed Framework collapsed, with North Korea pulling out of the Non-Proliferation Treaty.
It then tested a device this year, a test which is thought to have been less successful than Pyongyang hoped.
A key question for this new deal is whether it will lead to the North Koreans being entirely open about all their nuclear programme including their enrichment programme, about which very little is known to US intelligence.
When Libya offered to disarm in 2003 it gave up all of its programme, including equipment and details of suppliers - almost everything had been provided by the ubiquitous AQ Khan - and allowed inspectors from the International Atomic Energy Agency full access.
But the North Korean programme is far more advanced than that of Libya (which never produced any nuclear material) and in the Korean case it will be much harder to know if everything is being declared, making verification a very important part of the deal.
The step by step nature of this new deal is a reflection of cautiousness over North Korea's willingness to move forward.
But the fact that this time - unlike 1994 - other countries including China are party to the deal makes it more likely the North Koreans will stick to it.
Some analysts though remain cautious.
"This is a very small step," argued David Straub, former State Department director of Korean affairs.
"Whether it is a step toward North Korea's abandonment of its nuclear ambitions remains to be seen. It is, in any event, worth the effort, given the absence of better options."
"There is of course a very great risk that North Korea is simply using this as a way to avoid sanctions, obtain aid and drag out the nuclear issue until the international community becomes accustomed to its being a declared nuclear weapons state," he added.
North Korea's nuclear quest has essentially been about security and guaranteeing the survival of the regime.
Nuclear weapons are perceived as providing one guarantee but given the extreme poverty of the country, nuclear weapons also provide an important bargaining chip with disarmament offered in return for guarantees the regime will not be attacked as well as for economic aid.
An important unknown is whether Pyongyang will actually be willing to give up its existing weapons-grade nuclear material rather than just freeze the plants that can produce more.
The North Koreans may well not trust the US and therefore be nervous about giving up their most important bargaining chip without being absolutely convinced of their own security.
The success or failure of the deal will have implications for Iran
There has been a long, ongoing debate throughout the Bush administration on how to approach proliferation.
Hard-liners have consistently argued that direct negotiations leading to deals are dangerous because they risk rewarding proliferators for their behaviour by giving them something in return for breaking the rules.
This will only encourage further proliferation, it is argued.
More moderate voices have argued that negotiations are the only possible means for resolving the issue.
In the last year or so, moderate voices have gained the upper hand, primarily led by US Secretary of State Condoleezza Rice, and the US has engaged in six-party talks with North Korea and also offered the possibility of talks with Iran if it fully suspends its enrichment programme.
North Korea and Iran are very different cases - primarily because North Korea already had nuclear material whilst Tehran is still trying to develop the technology - but a deal with North Korea that holds may encourage those seeking talks with Tehran.
A deal which Pyongyang cheats on or which collapses for other reasons may strengthen those who say negotiation is the wrong approach.