CATECHISM OF THE CATHOLIC CHURCH
SECOND EDITION

Paragraphs 2310–2313

2310 Public authorities, in this case, have the right and duty to impose on citizens the obligations necessary for national defense.

Those who are sworn to serve their country in the armed forces are servants of the security and freedom of nations. If they carry out their duty honorably, they truly contribute to the common good of the nation and the maintenance of peace.

2311 Public authorities should make equitable provision for those who for reasons of conscience refuse to bear arms; these are nonetheless obliged to serve the human community in some other way.
2312 The Church and human reason both assert the permanent validity of the moral law during armed conflict. "The mere fact that war has regrettably broken out does not mean that everything becomes licit between the warring parties."
2313 Non-combatants, wounded soldiers, and prisoners must be respected and treated humanely.

Actions deliberately contrary to the law of nations and to its universal principles are crimes, as are the orders that command such actions. Blind obedience does not suffice to excuse those who carry them out. Thus the extermination of a people, nation, or ethnic minority must be condemned as a mortal sin. One is morally bound to resist orders that command genocide.