As a Faithful Catholic, I follow its teachings on war. War should be a last resort. Every peaceful means should be employed first.
In a just war, it can only be initiated to save life. It is for defense only. It can be preemptive if the threat of the loss of life is great but there must be proof of actions leading to harmful intent.
You are not to kill innocent civilians if possible. Life is sacred. Only those complicit in the unavoidable conflict can be targeted.
“Every act of war directed to the indiscriminate destruction of whole cities or vast areas with their inhabitants is a crime against God and man, which merits firm and unequivocal condemnation. A danger of modern warfare is that it provides the opportunity to those who possess modern scientific weapons — especially atomic, biological, or chemical weapons — to commit such crimes (CCC 2314).”