War

War, which is armed conflict between countries or nations, may be sometimes lawful and without sin. Three conditions are necessary for a justified war: (a) it must be waged by lawful public authority in defense of the common good; (b) it must be waged for a just cause; (c) it must be waged with the right intention, not vengefully nor to inflict harm.

It is not lawful for bishops and other clerics to fightin a war; such action is not in harmony with their place and their duties.

Ambushes are strategems of war; they are part of the normal conduct of war, and are not considered to be unfair tricks. Hence, if the war be just, strategems, including ambushes, are not wrong in themselves.

For the safeguarding of the common welfare, it is lawful to carry on the acts of a just war, and to wage fights, if need be even on Sundays and holy days.