Afghanistan has produced 85% of the world's opium for several decades, which is transformed into heroin in laboratories inside and outside Afghanistan, and sold later on international drug markets. The Taliban officially banned drug production until the invasion of the United States in 2001, but when they began to control since 2005 the very fertile provinces that are located in the southwest of the country, they allowed the farmers to expand into this activity and seized 10% of their income as 'taxes'. According to US intelligence reports, by 2011 the Taliban earned 400 million dollars a year from drug trafficking and in 2020 it is estimated that this figure had doubled.
Another source of income for the Taliban was the abundant illegal iron and copper mines that are found in Afghanistan, and by 2015 they already controlled 50% of the country. UN reports indicate that the smuggling of these mineral resources was equivalent to about 500 million dollars annually.
Last but not least, the third source of income for the Taliban come from donations from Pakistan, Gulf States, Iran and Russia. According to US reports, these accounted for 500 million dollars each year during the last decade. All this gives an approximate annual income of 2 billion dollars. The annual budget of the Afghan government is arround 5 billion dollars and 80% of it comes from international aid.
The international reserves of the Central Bank of Afghanistan, valued at $ 9 billion, are in US banks and these assets were frozen by the Joe Biden administration when Kabul fell, making it impossible for the Taliban to seize this money.
The new Islamic Emirate of Afghanistan will have difficulties accessing international financial markets due to the current blockade by the international community. Hence the importance for the Taliban to gain international recognition through persuasive public relations campaigns, and to get the support of China to finance infrastructure projects and exploit Afghanistan's natural resources and turn them into revenues.
It took the US three weeks to defeat the Taliban in 2001, and 20 years of an expensive presence in the country. How the fall of Kabul is possible, given that the government troups had officially 300,000 soldiers against 75,000 Taliban, and the US spent huge amounts of money in training them, has some explanations: 1. Many of those 300,000 soldiers are 'paper soldiers', this means people that just get into the army to have a salary but then run away. 2. The US never built good army instititions with clear command structures and career possibilities for soldiers that are found in any well formed army in the world. This made the Afghan army quite unprofessional and ill-organized. 3. The Afghan government is very corrupt and lacks popular support, so the motivation to fight against the Taliban is very low. 4. In Afghanistan, the society is mostly composed of clans from diverse ethnic groups and are very religious. When the Taliban attack a city, civil servants and their clans negotiate with them directly to avoid losses, bypassing thus the Afghan military command. 5. A big sector of the population relates much more with the radical islamist ideas of the Taliban than a secular, corrupt and puppet government imposed by foreign forces. Many of the civil liberties that were present since 2001 will be surely gone with a victory of the Taliban, and the countries that participated in the NATO operation are now regretting this outcome after spending so much resources in the country.