The fall of Afghanistan carried so many disasters for the whole area:

The mountains in the country made it almost impossible to invade, it represented a natural obstacle and that carried a big burden off the neighbouring countries. So, if Afghanistan fells, it meant that Pakistan, Iran and Iraq could easily fall as well.

The special strategic location of the country gave it extreme importance. It was in the center of Asia; whoever occupied it would enjoy a 360-degree view of the whole area around it. It was only a short distance to not only Pakistan and Iran, but also Russia and India. Above all, the occupying force would be near China, so controlling the whole continent was within reach.
The rough terrain in Afghanistan gave its people strength that you might not find in other countries; so, if these people were defeated, then defeating others would be even easier.

Muslims in that country had a very strong faith and a strong will for defending that faith. They found it hard to accept being occupied, which was made clear twice in their victories over the Mongolian armies. There was no doubt that overcoming these people would count as a great victory for any army.
Above all, the negative emotional effect on the Muslim nation and the positive boost that the Mongols got from their victory would have a far effect on future occurrences.

Thus far, the Mongols had gone from China to Kazakhstan, then Uzbekistan, then Turkmenistan; to Afghanistan, Iran then Azerbaijan to Armenia to Georgia and were very close to Iraq (map 6). All that happened in one year, 617 Hijra. Ibn Al-Atheer commented on that saying: “What those people (Mongols) have achieved in such a short time has no match in history, and I’m sure that whoever comes after us will have a hard time believing it. I don’t blame anybody for not believing the story; but if in doubt, check all that was written about it. People knowledgeable and ignorant all know about it for how famous and wide spread this story is.”

http://300035.dotdothktrade.tech/en/artical/21398/Fall-Afghanistan