When the Soviets announced that they were about to leave from Afghanistan in 1988, and they actually did so in 1989, Osama bin Laden, a rich Saudi, together with his Arab comrades, were in Afghanistan fighting the Soviets. In 1988 Osama bin Laden, with his best Arab comrades founded Al-Qaeda. By reading the Al-Qaeda’s story one can easily understand why this organization was founded.
After the Soviets left Afghanistan, a civil war broke out between the Iranians and the Pakistanis. The Iranians were supported by the Indians and the Pakistanis were supported by the Arabs of the Persian Gulf. Obviously the first aim of Al-Qaeda was to help their Pakistani allies fight Iran and take control of Afghanistan.
When the Soviets left Afghanistan they agreed with the Americans that none of them would militarily intervene in Afghanistan. The Chinese had fought the Soviets in Afghanistan too, but they did not want to get involved in a Muslim war fought by Iran, Pakistan and the Arabs, because no matter who China would choose to support, the other parties would support the Muslim Uyghur separatists in Xin Jiang, the Muslim province of China, in order to retaliate for China’s involvement.
Remember that the Iranians, the Arabs and the Pakistanis were all fighting the Soviets in Afghanistan, and therefore by supporting the Muslims the Chinese were safe during the period of the Soviet invasion. Safe in the sense that no Muslim militants would support Uyghur separatists in Xin Jiang. Actually during the Soviet invasion the Chinese were sending Uyghurs to their ally Pakistan, and Pakistan was training them to fight the Soviets.
Therefore the Americans, the Russians and the Chinese were not supposed to get involved in Afghanistan, at least not directly, and a civil war broke out when the Soviets left.
The Communist government that was left behind by the Soviets lasted from 1989 until 1992, when it was overturned by Iran’s allies in 1992, who were in turn overturned in 1996 by Pakistan’s allies, the Taliban, who were in turn overturned by the Americans in 2001, after the 9/11 attack and the refusal of the Taliban to allow the pipelines of Central Asia to reach India.
For the negotiations between the Americans and the Taliban for the pipeplines, and the Al-Qaeda attacks see “The Afghan Oil Pipeline and the US Negotiations with the Taliban”.
At the following map you can see the ethnic groups of Afghanistan.
Map Ethnic Groups of Afghanistan
http://www.cfr.org/afghanistan/taliban-afghanistan/p10551
With green you can see the Pashtuns, who were mainly supported by the Pakistanis and the Arabs. The Pashtuns are the larger ethnic group of the country. All of the Taliban are Pashtuns, or at least their overwhelming majority. But not all Pashtuns are Taliban.
With somon you can see the Shiite Hazara, a strong Iranian ally, and with brown the Sunni Tajics, who are of Iranian origin though, and normally they are Iranian allies too.
With purple you can see the Uzbeks of Afghanistan. Most Uzbkes have been part of the Northern Alliance, which was supported by Iran, India and Russia. But there were Uzbkes who allied with the Taliban too.
With blue, at the southern part of the country you can see the Baloch people. The Baloch people live in Afghanistan, Pakistan and Iran, and there are many among them who are calling for an independent Balochistan.
From all the above it is evident that the original goal of Al-Qaeda to help the allies of the Arabs in Afghanistan to fight Iran once the Soviets left the country. As long as the Soviets were there, the Muslims could achieve a minimum level of cooperation, since none of them wanted a communist Afghanistan. But once the Soviets left Afghanistan, there was a civil war about who would control the post-Soviet Afghanistan.