“Nothing is to be lost with peace; everything can be lost with war.”Pope Pius XII
"Catholics must work to avoid war and to promote peace. Nations should protect the dignity of the human person and the right to life by finding more effective ways to prevent conflicts, to resolve them by peaceful means, and to promote reconstruction and reconciliation in the wake of conflicts. Nations have a right and obligation to defend human life and the common good against terrorism, aggression, and similar threats. This duty demands effective responses to terror, moral assessment of and restraint in the means used, respect for ethical limits on the use of force, a focus on the roots of terror, and fair distribution of the burdens of responding to terror. The Church has raised fundamental moral concerns about preventive use of military force. Our Church honors the commitment and sacrifice of those who serve in our nation’s armed forces, and also recognizes the moral right to conscientious objection to war in general, a particular war, or a military procedure."
Forming Consciences for Faithful Citizenship 2007, 67
"Respect for and development of human life requires peace. Peace is not merely the absence of war, and it is not limited to maintaining a balance of powers between adversaries. Peace cannot be attained on earth without safeguarding the goods of persons, free communication among men, respect for the dignity of persons and peoples, and the assiduous practice of fraternity. Peace is 'the tranquility of order.' Peace is the work of justice and the effect of charity… Those who renounce violence and bloodshed and, in order to safeguard human rights, make use of those means of defense available to the weakest, bear witness to evangelical charity, provided they do so without harming the rights and obligations of other men and societies. They bear legitimate witness to the gravity of the physical and moral risks of recourse to violence, with all its destruction and death."
Catechism of the Catholic Church: 2304, 2306