“After the invasion of Afghanistan in 2001, remittances from the Gulf fell away. The Taliban needed new sources of finance. Mullah Mansour is thought to have developed a huge new source of income for the Taliban – along the way enriching himself and his fellow tribesmen. The movement he officially took over last year had been refashioned into what is, in effect, a multi-billion dollar drugs cartel.”

Source: Taliban instability could fuel opium trade – BBC News