There are already more than 100,000 international troops in Afghanistan working with 200,000 Afghan security forces and police. It adds up to a 12-1 numerical advantage over Taliban rebels, but it hasn't led to anything close to victory.
Now, the top U.S. and NATO commander in Afghanistan is asking for tens of thousands more troops to stem the escalating insurgency, raising the question of how many more troops it would take to succeed.
The 12-1 ratio may be misleading because two-thirds of the Allied force is made up of Afghans, who lack the training and experience. The Taliban usually fight in small, cohesive units made up of friends and fellow clansmen. A more meaningful ratio, then, might be 4-1 or 5-1.
Historically in guerrilla wars, security forces have usually had at least a 3-1 advantage.
Now, any strategist worth his/her salt will tell you that numerical supremacy within a theater of operations doesn't count for squat. It doesn't matter whether the US coalition outnumbers the Taliban by a ratio of 12-1, 5-1, or 3-1. What matters is what the ratio is when US forces are engaging the Taliban in tactical battles, such as those in Nuristan provinces. If the side with superior forces is spread out and trying to cover everything, then the side with fewer numbers and more agility has the combat advantage. This has happened time and time again through history.
These numbers and rations ought not to be considered in McChrystal's request for 40,000 more troops. What matters is what strategy is pursued - country-wide COIN operations, conducting combat operations, protecting "ink spots" and vital regions, or just training Afghan security forces and protecting the government. McChrystal didn't ask for enough to do a country-wide option, so I'm guessing that he's going for "ink spots" plus combat operations. President Obama seems to be leaning toward just doing the "ink spot" strategy, which might not require additional troops.
So ignore the talk about force ratios and troop increases - it's not relevant until a sustainable long-term regional strategy is developed and implemented. The real unanswered question remains, "How does this all end?"