I think two things helped ruin Afghanistan
1. The cold war
2. Pakistan's use of Islam for taking part in the cold war hoping to get traction and help in screwing India
If you read Sarila's deeply researched book on partition, the British favoured the idea of keeping tha "loyal north western mussalman" under their umbrella in order to thwart Soviet expansion. The same idea was ontinued by the Americans and Pakistan. There is a grat video of Pakistan PM Suhrawardy in the US asking for arms aid while throwing Pakistan's lot with the US in the cold war.
In PAF Air Commodore "Nosey" Haider's autobiography hementions the fact that even back in the late 1950s and early 1960 the PAF was atatcking Pashtun "rebels" - so a conflict has been ongoing since then, But Afghanistan had very good rlations with India (as it does now) and at partition NWFP would hev voted to join India if that was phusiclly possible. These are all known historic facts.
Jinnah himself was unhppy with the "moth eaten" Pakistan he got. One of the prime reasons for the 1947-48 conflict to take over Kashmir from Maharaja Hari Singh was that it was a way to get Pashtun tribesmen to attack Kashmir and take pressure off Pakistan. Thr tribesmen spent too much time raping women in Kashmir before taking Srinagar giving the Indian army time to push them back until Nehru gave a walk over, went to the UN and called for a cease fire.
But the Britis way of keeping Afghanistan quiescent was to have a buffer zone between Punjab and Afghanistan - the "NWFP" and the tribal leaders were all pad off/bribed. Still Afghanistan was a forward looking and progressive conuntry until the US and Pakistan coluded, using bin Laden and Saudi money to bring revolution to Afghanistan. Both the US and Pakistan are responsible here - not just the US.
The interesting part for me lies here:
1. Pakitan was set up as a "Paki" (pure) state for Muslims
2. the Pakistani constitution was revoked in favour of the "Objectives resoution" that sought to bring in sharia
3. Kashmir was attacked repeatedly in the name of being a Muslim majority state
4. Zia ul Haq joined the cold war stating that Pakistani support could be given ecretly (He said
"For Muslims it is alright to tell a lie for a good cause")
5. The "Taliban" were students of Pakistani madrasas trained in Pakistan and they too over Afghanistan
6. The same Taliban are now attacking Pakistan
So while the Islam connection is strong - it is not islam that cretaed the mess in Afghanistan, but Islam as used by Pakistani generals and leaders to play geopolitical games and ally with a US that does not give a flying fuk whether islam or Muslims are happy or are suffering as long as their Pakistani slave army is doing their job.
Note that all the games played by the Pakistani army and leaders did not get hem Kashmir or get them peace.
Afghanistan was abolutely fine with Islam until Pakistan was created as a western vassal state. In until Ranjit Singh Afghanstan always dominated what is Pakistani Punjab.
The British used loyal Mussalmans as a tool for their cold war. Those loyal Pakistani mussalmans used Islam to try and screw everyone. I am now happy to note that they are being exposed to true sharia by the Taliban. Pakistan is the problem. Proper Islamization of Pakistan will solve the problem.