Why does geography dictate that India and Pakistan stay involved in Afghanistan?

Question

This is a questions about Tim Marshall’s book Prisoners of Geography: Ten Maps That Explain Everything About the World.

Answer 1

Afghanistan, India, and Pakistan have always been and will always be tied together by a combination of geography and culture. Together, India and Pakistan make up the geographic body known as 'South Asia', while Afghanistan is part of 'Central Asia'. The South Asian sub-continent is isolated by a long string of enormous mountain ranges - the lion's share of which is formed by the Himalayas - that act like a near impenetrable wall separating South Asia from the rest of the Eurasian continent.

It is the portion of these mountain chains contained in Afghanistan, the Hindu Kush, that contain the most important passes through which trade and armies have entered the South Asian sub-continent from elsewhere in the Eurasian continent. As such, Afghanistan has been and always will be the land route by which people, good, and ideas reach India and Pakistan.