In 1923, two elderly women presented themselves at the front door of the British legation in Kabul. British they were by blood, but in name, language, religion and dress they were Afghans and the story they told, through an interpreter, was extraordinary, a small but revealing echo of Afghanistan’s bloody and bewildering history.

In 1842, Afghan tribesmen infamously massacred an entire British Army and their dependents as they tried to flee Kabul through the mountain passes in winter. Of the 17,000 soldiers, camp followers, women and children who set out for Jalalabad, only one man got through: Dr William Bryden, who staggered into the city, bleeding from multiple wounds, his horse dying beneath him.

In the space of a few horrifying days, Afghan bullet and sabre had claimed nearly three times as many lives as the attack on the World Trade Centre.

At the moment Dr Bryden was telling his dreadful story, jubilant Ghilzai tribesmen high in the mountains of the Khurd Kabul were picking their way among the multitudinous British dead when they came across two tiny baby girls beside their dead parents, still alive despite the intense cold.

Gently the tribesmen picked up these foundlings of history, and took them home. The children of their slain enemies were now treated as their own kin, and for 80 years they remained in the mountains. Until curiosity finally brought them down again.

As Sir Martin Ewans, the former Head of Chancery in Kabul, relates in his new history of Afghanistan: “They had lived all their lives as Afghans, but, in their old age, they had wished to meet some of their original compatriots.” Having done so, the old women left Kabul, returned to their homes, and were never seen again. Even their names have vanished from the record, but somewhere in the wilds of Afghanistan are some British Afghans, descendants of those survivors, living remnants of a romantic and terrible history.

The story is witness to the ferocity of the country’s past and the ethnic and religious complexity of the place, and to its intense tribalism. Adopted by the Ghilzai, the women had no desire to be British; once Ghilzai, they would always be Ghilzai.

The tale speaks of the ferocity of the Afghan fighter, but also of his generosity, his gentleness towards his own and his loyalty. It is this cast of mind, among potential allies as well as probable enemies, that now faces US and British forces in Afghanistan, a place often invaded but never subdued, easy to break into but harder to leave, where tribal allegiance and memories of bloodshed run through the land like the streams that lattice the Hindu Kush: the name itself means “Killer of Indians”, a memorial to the Indian slaves who died as they were dragged across the passes by their Afghan captors.

There is a strange, cruel pattern to Afghan history, where the coup is the accepted method of government transition, and fratricide merely the bluntest form of politics. It is a history of repeated invasion and permanent, chronic instability, compounded by internal tribal, ethnic and religious splits, coupled with an ancient warrior tradition, poverty, ignorance, corruption and multi-generational feuds buried so deep in the past that the roots have long been forgotten. The brutality of Afghanistan is matched only by its courage and its resilience.

It is a myth that Afghanistan repels all invaders, for the country has been successively overrun, by Persians, Turks, Greeks, Mongols, Arabs, Moguls, Sikhs, Russians and the British. Rather, it bleeds and baffles the invader until he stumbles home, thwarted by the Afghan mastery of guerrilla warfare, political duplicity, immunity to hardship, and skill at forging tribal alliances that evaporate the moment the foreigner is gone. War never ends here, but merely evolves and mutates, always on a local level, sometimes nationally, never simply.

The Afghan hill tribes lived in isolation, their tribal identities and mutual mistrust defining a fractured world; when the Pashtuns, Uzbeks, Tajiks, Hazaras, Aimaks and Turkmen were not fighting a communal enemy, they battled one another.