A US Marine at at a forward operating base in Mian Poshteh in Helmand Province
President Obama has announced that the US will send another 30,000 US troops to Afghanistan. Michael Codner, head of military sciences at the Royal United Services Institute, assesses what difference this will make on the ground.
President Barack Obama had the difficult challenge of not just speaking to his own nation. He also needed to send the right messages to the government of Afghanistan, to the Taliban and al-Qaeda, to allies, and to the world at large.
To that end, it will be important that subsequent rhetoric will develop issues - such as timelines for drawdown - with all of these actors in mind.
Mr Obama has, as expected, announced an increase in 30,000 troops to begin in early 2010.
This number is somewhat less than the 40,000 asked for by General McChrystal, commander of both Nato and US forces. However, he expects other nations to increase troop levels, and the additional 10,000 is feasible.
For the UK, Gordon Brown has announced an additional 500, taking its total to 10,000 including 500 special forces and enablers already in theatre.
The German government has indicated an additional 3,000.
Leadership of this sort by the larger European nations could prompt smaller nations to bolster their stakes in the "strategic bargain".
There is, of course, the problem of some nations' plans to withdraw forces - Canada and the Netherlands in particular - bearing in mind that they have been prepared to contribute to the more violent southern provinces.
Pattern of integration
It's worth remembering that the US contribution - which will reach 100,000 - will be no larger than the Soviet presence at the height of its occupation of Afghanistan. And that resulted in failure.
US troops must halt the Taliban while Afghan forces are built up
Of course, troop numbers alone are not the answer to the problem, as the Obama and McChrystal strategies acknowledge.
There must be a surge in the civilian contribution. But they are a sine qua non, and the total US and ISAF military presence will begin to approach some historical levels that have delivered progress.
In particular, armed forces must in the short term halt the momentum of the Taliban. They must also dominate further attempts at escalation while the Afghan military and police security forces are expanded to the 200,000 plus that Mr Obama wants.
But the quality of Afghan security forces is every bit as important as quantity.
How will the 30,000 new US troops be made up? Mr Obama did not announce this detail, but it is understood that they will include combat forces, engineers and aviation.
US Marines will be deployed to Helmand Province, a particularly problematic province, alongside British forces. What the command arrangements will be is not yet known.
However, there is a clear pattern of greater integration between US and British forces. This indicates more emphasis on US rather than Nato leadership in Afghanistan, with the UK in a strong supporting role in command of the area known as Regional Command South (RC South).
A specific problem in RC South is Kandahar, the second largest city in Afghanistan and the Pushtun capital, where the Taliban have been effective in gaining control.
Clearly this will be a priority for US reinforcements, bearing in mind the probable withdrawal of Canadian forces who currently have responsibility.
One option might be a full-scale attack along the lines of the Second Battle of Fallujah in Iraq. Decisive events of this kind can be very effective in reversing enemy momentum and convincing local populations of progress.
However there could be large numbers of civilian casualties, which could send the opposite message of an unwelcome victor and weaken support for the US in Europe and globally.
President Karzai must show commitment to change
Other options might be a more incremental approach, with the accompanying challenge of the July 2011 timeline. Or an attempt to limit Taliban influence in the city, and isolation from the surrounding region if this is realistic and feasible.
From a military viewpoint, there are three problems with Mr Obama's strategy.
The first is whether the force levels are enough to turn the tide against the Taliban and win Gen McChrystal's "short fight" by July 2011. This is when Mr Obama has announced that withdrawal of US forces will begin, assuming transition and transfer of responsibility to Afghan forces takes effect.
Second, this very issue of a stated date for drawdown could play into the hands of al-Qaeda and the Taliban, allowing them to bide their time before returning to the offensive - a common feature of insurgencies.
Importantly, Mr Obama stated that the July 2011 date would take "into account conditions on the ground".
Finally, there is the matter of President Karzai's commitment to change - to deal with corruption and criminality and to expand and improve Afghan security forces.
This uncertainty exposes the paradox of timelines. Unless Mr Karzai and his government have deadlines to face, there is every possibility of a pattern and culture of dependency on the US and international support.