There are 2 passes from British India’s North West Frontier into Afghanistan.
The more famous and shorter pass is the Khyber Pass from Peshawer to Jalalabad and then to Kabul. This pass is 35 miles long. {p125 Greenwood}
The longer route is via the Bolan Pass to Kandahar. This pass is 70 miles long. {p 162 Dalrymple}
Here are 5 excellent books on Afghanistan.
Dalrymple’s book is on the origin of the Great Game, the tussle between two ancient Afghan families for the throne, the reckless gambit by the British to install Shuja Shah on the throne via the Army of the Indus, the ignominious retreat to Jalalabad and the subsequent revenge via the Army of Retribution.
Lady Sale is her memoirs of the Cabool retreat, her subsequent capture and rescue by her husband Brigadier Sale.
Greenwood is on his service in the Army of Retribution.
Both books on Khyber Pass is on the history for control of this famous pass.