Should a robber break into my house, and with a dagger at my throat make me seal deeds to convey my estate to him, would this give him any title? Just such a title, by his sword, has an unjust conqueror, who forces me into submission. The injury and the crime is equal, whether committed by the wearer of a crown, or some petty villain.
Over those then that joined with him in the war, and over those of the subdued country that opposed him not, and the posterity even of those that did, the conqueror, even in a just war, hath, by his conquest, no right of dominion: they are free from any subjection to him, and if their former government be dissolved, they are at liberty to begin and erect another to themselves.
For no government can have a right to obedience from a people who have not freely consented to it; which they can never be supposed to do, till either they are put in a full state of liberty to choose their government and governors, or at least till they have such standing laws, to which they have by themselves or their representatives given their free consent, and also till they are allowed their due property, which is so to be proprietors of what they have, that no body can take away any part of it without their own consent, without which, men under any government are not in the state of freemen, but are direct slaves under the force of war.
Nor can such an usurper, or any deriving from him, ever have a title, till the people are both at liberty to consent, and have actually consented to allow, and confirm in him the power he hath till then usurped.

Popular pages: Locke's Second Treatise on Civil Government