In 1688, William of Orange convinced the English Parliament to oust the current King James VII of Scotland and of England and install William himself as regent. At the time, England and Scotland were a boiling cauldron of national and religious animosities, not only between the two countries but amongst political factions and the clans themselves.
A minor event in history was the appropriation of MacDonald property by the Campbells. The MacDonalds felt free to to reclaim cattle which they still considered their own. The Campbells called them reivers and no love was lost between the clans.
Then King William demanded an oath of loyalty by all clan chiefs with a deadline of 1. January 1692. MacDonald Clan Chief MacIain of Glencoe, leaving this distasteful necessity to the last moment, made his way to Fort William on 31. December 1691. Glencoe presented himself to Colonel Hill the governor, asking him to administer the required oath of allegiance. Hill told Glencoe that he must go to Inverarary, which wasn't easy in deep mid-winter snow, and mountainous terrain, so he was late. This appears to have been a premeditated plot, involving secret letters, ignored letters of free passage and other skullduggery by the current political officials. They gleefully planned to make an example of the Ian MacDonalds at Glen Coe and the Campbells were not in the least reluctant to assist in the execution of this plan.
With instructions to kill every man of the Glen Coe clan under 70 (approximately 200), Campbell of Glenlyon and some 128 soldiers, of various clans, including Campbells, called on MacDonald, said they were in the area to collect taxes and asked his hospitality. For 12 days they had a spontaneous ceilidh, ate the MacDonalds' winter food supply, drank to each other's health and made marriage plans between the young ones.
Exactly according to plan, at five o'clock on the morning of 13. February 1692 Campbell of Glenlyon and his soldiers rose from their beds to massacre their hosts.
They managed to kill "only" 38, including some women, children and an 80 year old man, but some escaped and women and children were sent naked, into a sudden blizzard, from their razed and looted homes.
This event is still much debated today
The monument to the fallen MacDonalds is situated in the Glencoe village, and MacIain was buried on the island of Eilean Munde, in Loch Leven, near the entrance to the Glen.
I would like to add a something to your notes regarding the swearing of allegiance to King William.
Because the chiefs at that time were loyal to King James they could not swear allegiance to a foreign King. The clans continually informed James that unless they swore allegiance to William they were putting their people at risk. King James resisted giving permission to the clans until the last possible moment but eventually relented.
Glencoe being remote, was one of the last to get this dispensation and upon getting permission, from King James, MacIan immediately made his way to the Fort. The rest is as you tell it.
One other point I would like to make is that of recent years, the Campbells deny all responsibility citing the fact that an English regiment carried out the massacre. This is true, but this particular regiment was raised in Argyll-shire, the seat of the Campbells, and Campbells and their Septs were in the majority of the troops who carried this out.
This incident is now being cited as the reason for collapse of the Clan system. Not because of MacIan's so called stubbornness, as for many years was given as the cause, but of the betrayal of the clans by the Campbell.
No longer could a Clan be trusted !