But US is going out of Afg in 2014 and Pakistanis are the most happy bunch about it :'(
That's why I used the word "interest" instead of presence. Here is a look at the bigger picture:
It is well known that US has a high standard of living, but according to GDP break down in 2012, 79% of the US GDP is, in fact, service industry, real estate, etc. In other word, virtual economy. Its actual industry product is less than 20% of the GDP and less than that of China's industrial production even in nominal term. In PPP, US actually has less than 50% of China's industry production. Meanwhile US is also sitting on one of the largest trade deficit. So where did US get the money and economy to maintain its high standard of living?
The answer to that is US can do it because US dollar is the de facto international trade medium. If two countries do not have direct currency swap, then the only way for them to do business is through US dollars. This means US dollar is huge demand and the US can literally print money to support its economy. However, there is a downside to this. In order to maintain US dollar' status as international trade medium, no other currency have to be able to challenge it. For example, Japanese Yen used to have the potential to challenge it, then Plaza according happened and Japan is in the lost decade. Euro could have challenged it and the US credit agencies down-rated European countries. Heck, Mubarak and Gaddafi tried to organize an African Union and we all know what happened next.
Now what does Afghanistan has to do with this? Well, one of the main reasons US dollar is used as international trade currency is because all petroleum trade with OPEC have to happen using US dollar. (OPEC tried to release their own currencies, let's just say it didn't work out well.) Afghanistan is important because it sits right between Eastern Asia powers and OPEC. If Afghanistan went outside US control, then OPEC would be coming directly in contact with Eastern powers and it is possible for US to lose control over them. (This is why US supported Taliban in its fight against USSR. In fact, between US trained Taliban and US invasion of Afghanistan, there is only a few year of window in which Afghanistan is NOT under US control or influence.)
And let me stress again, if US want to operate in Afghanistan, they have to have the cooperation from Pakistan. This is why US never slapped serious sanctions against Pakistan all these year despite the friendship between Pakistan and China.
