It is a story of many things: enterprise, war and a schoolboy's homesickness. For around £600,000, the British Museum has acquired a collection of rare American Indian artefacts from Stonyhurst public school in Lancashire - a collection made of wood, skin and bone, which at first seems rather unprepossessing. Yet after a morning's explanation, it transported everyone back to the era of the Wild West.

The first character in the tale is John Mullanphy, an enterprising man from a village near Enniskillen in northern Ireland, who emigrated to the newly independent States in the 1790s. He set up as a cotton trader, largely in the Midwest city of St Louis. Mullanphy would buy cotton at next to nothing per bale, ship it over to Liverpool and sell it at the cotton exchange for a great deal more. He had 11 children, eight of whom survived, and became known as "the first millionaire of the American west". Mullanphy was clearly quite a character: at the Battle of New Orleans in 1815, his cotton bales helped defend the city against the British army.

In 1821, at great cost, he sent his only son, Bryan, to Stonyhurst. Presumably Mullanphy had seen the Lancashire cloth mills and felt his son would be at home there. He wasn't. His letters, now in an American archive, tell of his misery, and he went back to St Louis for a respite. When he returned to Stonyhurst, he brought with him some things that had been given to his father by "contacts". Described by the school archive as "Sioux items", they include pipe stems, rawhide shields and a deerskin map.

Our presentation was led by Jonathan King from the British Museum's department of ethnography and JoAllyn Archambault of the Standing Rock Sioux tribe, who was brought up, as she put it, on a "res" (Indian reservation) and who now runs the American Indian programme at the Smithsonian Institution in Washington, DC. So what do the experts make of this stuff; was it stolen from the Native Americans? Even more embarrassingly, have we stolen it from the States? Ever sensitive about what one might call a "Parthenon" issue, the museum went out of its way to explain that these items were from an "innocent" time when Indians, at least those in the Midwest, were on an equal footing with the white settlers and would give things such as shields and pipes to mark mutually beneficial land or trade deals. "They represent what we call 'Peace and Friendship Treaties'," said Archambault. "They were probably a precursor of later treaties." When things turned a bit more cynical? "When all the land was stolen from the Indians."

OK, so there are no metaphorical bloodstains on the collection. But shouldn't it be repatriated? "We have about two million American Indian artefacts in Washington," said Archambault coolly. "Most of which come from the time when Indians were put into reservations. Early items such as these were usually given to ex-colonialists or collected by them. It's fitting that they are in Europe."

When you look at the collection, a foreign, unusual image of America arises: an America half in wilderness, still being plotted and mapped; a country so innocent to industry that it had no cloth mills of its own; a place where one might expect boiled catfish for dinner, and where diplomacy with other races was marked by pleasantries and freely exchanged gifts.