By Yang Qingchuan

When it comes to Afghanistan, no great power has ever succeeded in controlling that country.

These days, as US President Barack Obama is weighing hard choices on a very likely further increase of troop levels in Afghanistan, the "graveyard of empires", he is very aware of that part of history.

After Stanley McChrystal, the top US commander in Afghanistan, submitted a bleak assessment of the nearly 8-year war, now it's for the president to make the decision.

But the choices are hard to make. It's obvious that more troops and other resources are needed to help Obama's new strategy to work, but he is also confronting a growing anti-war public sentiment here at home, in the fear that the country will eventually be trapped into Afghanistan like all those military powers in history.

No matter how soon the president will announce a further troop increase and a change of tactics, the conflict, which has already become "Obama's war", has no end in sight and the prospect is far from clear, analysts said.

More troops, resources 

Although McChrystal didn't make any formal request for additional troops in his report, but the White House clearly opened door to such possibility.

Commenting on the report, White House spokesman Robert Gibbs said on Monday that a formal request for more troops or other war resources will be coming in next few weeks.

He used the word "under-resourced" repeatedly to describe US efforts in Afghanistan.

"For many years, our effort in Afghanistan has been under-resourced politically, militarily and economically," he said.

The New York Times and other US newspapers said that could be interpreted as an euphemism for "we need to put more troops and other resources there".

In a public statement on his report, McChrystal said "the situation in Afghanistan is serious, but success is achievable".

He called for a "revised strategy", greater "resolve" and a "unity of effort" to salvage the war.

The report's recommendations include a shift in military strategy to protecting local population from simply fighting the insurgents, speeding-up training of the Afghan military and double its size.

Although he stopped short of requesting more troops but analysts said protecting the Afghan population and training more Afghan troops will surely require more US troops and military trainers.

When Obama announced his new strategy for the war in March, he said the goal is to "disrupt, dismantle, defeat al Qaida" and the Taliban forces which provide safe havens for terrorists.

Obama has already planned to increase troops in Afghanistan to 68,000 this year.

But military analyst Frederick Kagan said that number is not enough to achieve his objective.

The US Army doctrine says that to effectively protect local population in an insurgency, it requires one soldier for every 50 civilians. In Afghanistan, it means 320,000 troops are needed.

However, with 68,000 US troops, other NATO forces, Afghan troops, it only adds up to 270,000.

Anthony Cordsman, a scholar who advised McChrystal in writing his report, said many experts believe the commander may at least need 3 more brigades, or some 10,000 additional troops.