CCC 2265

Legitimate defense can be not only a right but a grave duty for someone responsible for another's life. Preserving the common good requires rendering the unjust aggressor unable to inflict harm. To this end, those holding legitimate authority have the right to repel by armed force aggressors against the civil community entrusted to their charge.⁶⁶ St. Thomas Aquinas, STh II-II, 64, 7, corp. art.