The Khyber Pass is the main route between Pakistan and Afghanistan. The pass itself is entirely in Pakistan. The nearest major cities on the route that goes over the pass are Jalalabad in Afghanistan and Peshawar in Pakistan, with Torkham as border crossing point.
Crossing the Khyber has always been something of an adventure. Even in peacetime, this was a fairly wild region where banditry and tribal warfare were part of local history and almost every adult male went armed. Today, with the region in the center of an ongoing armed conflict, it is clearly far too dangerous for most travelers.
The area is inhabited by Pathans or Pashtuns, rather fierce Pashto-speaking hill tribes. On the map, it was a border region of the British Raj and is now part of Pakistan, but neither the British nor the Pakistani government have ever fully controlled it; Pathan tribal chiefs run everything. Pashtun territory spans the border. 60% of them live in Pakistan, 40% in Afghanistan. In Afghanistan, they are the largest ethnic group at 40-odd% of the population and have often dominated government and business.
The Pashtuns have twice defeated the greatest armies of their day. When Alexander the Great wanted to cross the pass, he could not manage it until he bribed some Pashtuns to assist him against others. At the height of British power in Queen Victoria's reign, the Khyber was the border of the Raj; Britain fought several wars in the area and never completely subdued it. In the first Afghan war (1839-1842), a force of 16,000 (4500 soldiers plus grooms, cooks, etc.) went in and one man came out alive.
Pashtuns were also recruited into the British military, where many of them were excellent soldiers. There were several famous regiments, mainly cavalry, that were entirely Pathan except for the British officers. Today, the Pakistani military includes many Pashtuns.
The Pashtuns provided most of the adherents of Taliban. That movement originated in Pakistan and only later — with help from the CIA and Pakistani Intelligence, who saw it as a counter to Mujahideen warlord power — took over Afghanistan. Among its strongest influences are the traditional Pashtun code of ethics, Pashtunwali, and the Deobandi branch of Islam. Deobandi is a fundamentalist Sunni movement emphasizing Shari'a Law which arose in India in the 19th century and is now common among Pashtuns. At one time it was heavily funded by Saudi Arabia because it resembles their own Wahhabi style of Islam and was seen as a counter to the influence of Shi'a Iran, especially in Afghanistan.
Since 1980, Pashtuns have been fighting Russians, various other Afghans, American and allied forces, the Pakistani army, and sometimes each other. Many — both pro and anti-Taliban, and on both sides of the border — are still (2014) fiercely resisting various efforts by US and allied forces and/or the Afghan and Pakistani governments to control their area.
Closed to foreigners?
A few travellers have reported lately that they were refused permits to travel from Peshawar to the Khyber Pass, and told the only option was flying, based on perceived heightened threats to foreigners: others have said that only those travelling through and crossing the border are issued permits. In any case, be prepared to make alternate plans if you must visit Afghanistan.
Except for trails which only locals can use safely, the only way in or out is via the main road through the pass.
From Peshawar to Torkham (the border town) you are required to obtain a permit and travel with an armed guard.
The pass is on the Istanbul to New Delhi over land itinerary, though the current recommended route avoids it.
The pass forms part of the Grand Trunk Road, a historic highway that runs through parts of four countries — Bangladesh, India, Pakistan and Afghanistan.
At the top of the pass is the town of Landi Kotal, famous for smuggling everything from consumer electronics to AK-47s. Attractions for the intrepid tourist include weapons factories and hashish warehouses.
This area, as of early 2015, has been definitely not safe for over a decade. Avoid it if you can; see War zone safety for suggestions if you cannot.