"The Soviets had some at maximum 100,000 troops in Afghanistan but there were also some 300,000 more or less reliable Afghan forces available. In total they had the 400,000 soldiers the leaving NATO commander recently said were needed in Afghanistan. They still lost the war. The 'west' now has some 70,000 troops in Afghanistan and the Afghan army has about 80,000 soldiers". Source: Moon of Alabama Blog.
Oh, there is something else relevant: The Soviets could just march into Afghanistan because the two countries were contiguous sharing at that time a long border. US/West and Afghanistan are as connected as Alaska to Africa.
General McChrystal wants another 40,000 troops. That would bring the US troops strength to match the Soviets when they were trying to subdue Afghanistan. So, the US can win when the Soviets failed with a supply line across continents and seas?
If you still think so, read this latest report here.
This report does not even touch on those Al Qaeda guys living the caves beyond the deadly power of US airpower.