By Alastair Leithead
BBC News, Kabul
However committed the international community is to Afghanistan's future, it has to keep a firm eye on an exit strategy.
The Afghan National Army faces huge challenges
It will, of course, take years to bring stability after decades of war, and the primary concern is security - how hard international forces can hit the insurgents this year and how well Afghanistan's own police and army perform.
The announcement of new American money will certainly give the fledgling forces a serious leg-up.
The pledge of $8.6bn (£4.39bn) over just two years to build the Afghan security services is more than twice the entire budget America has come up with in the last five post-Taleban years.
It will buy arms and equipment, mentoring and training, and will attempt to create a force capable of securing Afghanistan itself, but that is a big ask.
Money has already been flowing into the Afghan National Army (ANA) coffers and there are a significant number of Afghan soldiers fighting alongside the 40,000 or so international troops, but progress has been slow and they have a very long way to go.
And the Afghan National Police (ANP) are even further behind with training and equipment.
The military strength in fighting the Taleban insurgency is Western air power and artillery, and that is something the extra cash is going to struggle to bring in the short term.
The fact that the best modern military machines cannot defeat the Taleban speaks volumes, and shows how much more difficult it is going to be for the Afghans.
But Defence Minister Gen Abdul Rahim Wardak is confident the new commitment will make all the difference.
Speaking earlier this week, when the pledge was being prepared, he was thankful the international community was finally listening to him, and finally providing the resources needed.
"All this time we have been trying, but we have been armed with 30-year-old weapons - all used during the war with the Russians," said Gen Wardak.
"The army has not been provided with the combat enablers and the result is a force that is not effective.
"I think some of the assumptions about the security threat and capabilities of the ANA were not correct - as a result of this re-assessment the international community now knows we have a firm foundation to build on."
The extra American troops - forces prepared to fight, however hard it might be - will also help bolster Nato operations.
The last thing that 3,200 soldiers from the 10th Mountain Division want to do is to stay in Afghanistan for another four months when they were preparing to go home.
But their continued presence will give the Nato commanders the extra troops they were looking for - indeed the troops outgoing International Security Assistance Force (Isaf) commander Gen David Richards said would be needed to finish off the insurgency this year.
General David Richards is leaving in optimistic mood
It perhaps questions the wisdom of such strong statements when many - including the outgoing American commander in Afghanistan, Lt Gen Karl Eikenberry - predict a "violent spring."
The timing of the US announcement is no doubt to try to pressure Nato or partner countries to dig deep and come up with their own way of bolstering the Afghan effort.
Britain may well send a few hundred more troops, but persuading countries who are in Afghanistan to deploy to the most dangerous places, or to reinforce the mission, is not going to be easy.
Nato has promised to launch its own spring offensive - ahead of the insurgents who are widely thought to be preparing for a renewed push after losing some momentum in their campaign at the end of last year.
At the beginning of 2006, Nato and the US-led coalition certainly lost ground to the Taleban - it was a long and bloody summer.
But Gen Richards is brimming with optimism as he prepares to clear his desk and head home.
He doubts the Taleban spring offensive will come and is confident his forces have the upper hand.
Many doubt this confidence, but what is more worrying is on the political level.
Corruption and the lack of government structures are huge concerns - indeed few ministries have the capacity to spend all the aid money that is flooding in.
Afghans are often more concerned about how rotten the system is than about security.
Expectations, sky high when the Taleban were forced out in 2001 and the world rallied behind the Afghan people, are not being met, and there is a thickening cloud of disappointment drifting across the country.
Development is slow to filter through, and grand plans costing billions of dollars are all very well, but when poor Afghan people do not see their lives getting better they start feeling let down.
But if they can take one thing from the American pledge, it is that the international community is not letting Afghanistan down as yet - there is still a commitment to try to bring the country back on track.