The last time I checked, the Islamic State's capital was in Raqqa, Syria. The other main cities it holds are Mosul, Iraq; Fallujah, Iraq; and Palmyra, Syria. All told, the Islamic State has tens of thousands of fighters controlling maybe five million people in those areas. 

But never mind that. Let's drop a bomb on their caves in some remote valley in mountainous Afghanistan, 5000 kilometers away. What could be more obvious, strategy-wise?. Not to mention the fact that the GBU-43's have passed their 'use before' date.