In the third act of Julius Caesar, after Mark Antony gives way to grief and admits a desire for revenge for the murder of his friend and emperor, he then predicts war with the words, "Cry havoc! And let slip the dogs of war."
To cry havoc, in the Shakespearean context, meant to give an army the order to pillage. Since that time, the phrase has come to signify "to sound an alarm or warn of disaster."
To let slip the dogs of war is to unleash the horrors of war. We can thank Shakespeare for coming up with the dogs of war figure of speech that refers to wartime devastation. Over the centuries, dogs of war also developed into a synonym for mercenaries, soldiers-for-hire whose warrior-ways are governed by their wages.
Havok was an old military command to massacre without quarter. The origin of the word is uncertain although it is of possible Germanic origin. In the 9th year of the reign of Richard II, the cry was forbidden on pain of death.
