Locke starts off by stating that an unjust conqueror never has the right to rule the conquered. Unjust conquest is always unjust in Locke's model, whether by petty thief or a despot. Locke then moves on to make provisions for the cases in which there is a lawful conquest (which he does not yet define). In lawful conquest, "The conqueror gets no power by his conquest over those that conquered with him." In other words, those that help the conqueror conquer cannot suffer from having given their aid; rather, they should benefit from it.
The conqueror gets despotical power over those who relinquished their rights and lives by waging unjust war. Locke notes the important limitations to this power carefully. The conqueror only gets power over the government that waged the war, not the entire populace, unless the populace explicitly sanctioned its government's unjust war. It would be unnatural for the conqueror to acquire despotic rights over a people who have done nothing to deserve the loss of their freedom. Locke goes on to note that the unjust use of force, in any context, puts one person into a state of war with another.
Locke then continues his explanation of the limits of the lawful conqueror's power. Recalling the prior argument that a father cannot forfeit any of his children's rights, and remembering that an aggressor's children have a prior right to the aggressor's estate, a conqueror cannot seize the property of an aggressor. The just conqueror's right extends only to the lives of the aggressors, not to their estates, since others have a prior claim and right to the latter.
Locke points out that this may necessitate certain instances in which a conqueror must "remit something of his full satisfaction." Despotic power, the power of a just conqueror over an unjust aggressor, would indeed include seizure of that aggressor's property, if no one else's rights were bound to that estate. But since the rights and survival of the aggressor's family may depend on the estate, the just conqueror must forego his lesser right to the property in the face of the family's prior, stronger claim. The just conqueror, by ignoring these claims, can become an unjust aggressor.
Chapter 17 gives quick attention to usurpation, which Locke describes as domestic conquest. Usurpation is simply a change of leadership, not of the forms of rules and government, and is not right unless sanctioned by the people. A usurper has no just right to the power he has taken until the people freely confirm him as a leader.
This is the only point in the Treatise in which Locke deals with just action that could be considered in any way aggressive. It is very telling, then, that this just action quickly becomes unjust if it extends beyond the limits Locke allows for righteous conquest. Locke's ideas of righteous conquest are what one might expect--retribution rooted in the law of nature, and a protector of the victim's property, privileged over his life , on the basis of his family's natural rights to that property. Locke simply and elegantly extends his principles and ideas to the question of a successful war.