State of War and the Right to Self-Defense

Daily Dabble in the Classics, John Locke, 1690

It is the unjust use of force then, that puts a man into the state of war with another; and thereby he that is guilty of it makes a forfeiture of his life: for quitting reason, which is the rule given between man and man, and using force, the way of beasts, he becomes liable to be destroyed by him he uses force against, as any savage ravenous beast, that is dangerous to his being.

Source: John Locke, Second Treatise of Government, Ch. 16, Of Conquest