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
http://www.christusrex.org/www1/CDHN/fifth.html#SAFEGUARDING