Social Teachings of the Catholic Church
: Peace and War
"Evils and injustice accompany all war", and because of this, we must strive to free ourselves "from the ancient bondage of war."
Thus, all governments must strive to avoid war. However, governments also have the right to "legitimate self defense", if all efforts at peace have failed.
The Church outlines the criteria for a legitimate self defense, the so called "just war doctrine":
"The arms race
is one of the greatest curses
on the human race
and the harm it inflicts on the poor
is more than can be endured
Condensed from The Catechism of the Catholic Church