For various reasons,
In 1689 the "Glorious Revolution" had replaced James the 7th (and 2nd) on the Scottish,English and Irish Thrones by William of Orange who was the head of the Dutch republic. This was a fairly bloodless episode in England since the Protestant William was prefered to the Catholic James but in Ireland the mostly Catholic population supported James and in Scotland the again mostly Catholic Highlands also rose to defend the King, it's important to note that the Scots lowlands were much more in favour of William. This lead to various battles and events running on in Northern Ireland until the present day. However for our purposes by 1692 the minor civil war was over and James had fled to France, William then offered a pardon to those Highland Clans and Families which had fought for James and promised no action against them if they would come to a Magistrate (a judge and government rep) and swear loyalty to the (new) King before Jan 1st 1692.
Alastair Maclain the Chief of the Glencoe branch of the Clan McDonald left it to the last minute to go and make his oath. MacIain had been waiting for permission from King James to make the oath, this took a long time to arrive and for the news that James had granted it to be passed around. Once he decided to make the oath he then struggled to find a magistrate or officer to take it in front of resulting in him being 3 days late doing it.
Despite this he returned home thinking that he and his clan would be fine. However the Lowland Scots government and the old clan rivalries combined and using the excuse of his late oath the massacre was ordered, partly as an example to others but mostly to settle old scores.
The Massacre of Glencoe was created in 1971.
The Massacre of Glencoe - 1971 is rated/received certificates of: UK:PG (video)
The so-called 'Massacre of Glencoe' took place in 1692.
Mcdonald clan and campbells clan
The Campbell's massacred the MacDonalds at the Glencoe Massacre that took place in the Scottish Highlands in 1692. The Campbell's, who were acting on behalf of the government, attacked the MacDonald clan resulting in the deaths of many of its members.
Massacre of Kondomari happened in 1941.
Bleiburg massacre happened in 1945.
Aranthalawa Massacre happened in 1987.
Palawan Massacre happened in 1945.
Kucheng Massacre happened in 1895.
Kibeho Massacre happened in 1995.
Itaba massacre happened in 2002.