The Pashtun are the main tribe in Pakistan's Northwest frontier province and make up about half the population of Afghanistan. They are considered to be one of the oldest tribes on earth, and their tribal laws date back thousands of years.
Their strictest laws - the 'Pashtu Wali' or Code of Life - include 'badal', when members of a tribe must revenge a wrongdoing; and 'milmasthia', where the tribe must serve a guest and give sanctuary to anyone who asks for it, even if they are an enemy, which is why the Taliban won't hand over bin Laden.