53. St. Brice's Day Massacre, England November 13, 1002

 King  Æthelred of England really did not have the wherewithal to successfully deal with the Danish/English tension that he had inherited with the throne, which had been caused by Viking raids for about 100 years,  notably established by what the English called The Great Heathen Army, which took over much of England.  Oh, too bad. One solution, he thought, was to kill off all the Danes in England.  This did not work. For one thing, the Danes did not in fact get killed off, though the English did kill some of them -- notably in Oxford, where they burnt the church down with Danish settlers gathered inside. For another thing, the Vikings invaded again, not long after the Massacre. The throne of England went back and forth between the English and Danes, after that, for some decades, until, in 1066, the Normans would invade and take everything over, establishing a NEW Viking dynasty, one which spoke French. And liked to write history.