Blood and Soil
In his book "Blood and Soil" Ben Kiernan states that imperial powers have often resorted to committing genocidal massacres in order to control difficult minorities within their empires. As an example he describes the actions of two Roman legions which were sent to Egypt in 68 AD in order to quell Jews who were rioting in Alexandria in support of Jews who were taking part in the First Jewish–Roman War. The Roman governor Tiberius Julius Alexander ordered two legions to massacre the inhabitants of the Jewish quarter, which was carried out to the letter, sparing none whatever their age or sex. The massacre ended after about 50,000 had been killed when Alexander, listening to the pleas of some yet to be killed, felt pity for them and ordered an end to the killings.