Douglas Lackey, “Just War Theory,” in Larry May, Applied Ethics: A Multicultural Approach, Prentice Hall, 2011, 5th ed., pp. 262-269.
Lackey argues for the view that under certain conditions it is permissible to go to war. The conditions for determining whether a war is just are:
1) The war is declared by a legitimate authority. Public, not private, bodies must make the declaration of war.
2) The war is declared for a right intention or a just cause. Self-defense is a right intention, but colonial expansion and wars to bring a better way of life are not.
3) The declaration (jus ad bellum) and the execution (jus in bello) of war adhere to the rule of proportionality. War is a last resort.
4) In the execution of the war, the principle of discrimination must be observed. Killing must be directed at combatants (non-innocents), not at noncombatants (innocents).
5) The war is followed by a just peace. Tyrannical rule may not be imposed on a defeated country.