Our principle is, and our practices have always been, to seek peace, and ensue it, and to follow after righteousness and the knowledge of God, seeking the good and welfare, and doing that which tends to the peace of all. All bloody principles and practices we do utterly deny, with all outward wars, and strife, and fightings with outward weapons, for any end, or under any pretence whatsoever, and this is our testimony to the whole world. ...
From Declaration to Charles II, 1660
Do we have to continue to tolerate the killing of innocent civilians, or war itself, as a means of settling disputes? War has been illegal since 1929. As it says in Wikipedia "The 1928 Kellogg–Briand Pact was concluded outside the League of Nations, and remains a binding treaty under international law".
Treaty for the Renunciation of War
(The Kellogg-Briand Pact or The Pact of Paris)
Signed at Paris 27 August 1928 and ratified by the USA, UK, Australia, Canada, Czechoslovakia, Germany, India, Irish Free State, Italy, New Zealand, South Africa on 2 March 1929 and later by Poland, Belgium, France, Japan, and (by instruments of adherence) forty other countries
The High Contracting Parties solemnly declare in the names of their respective peoples that they condemn recourse to war for the solution of international controversies, and renounce it, as an instrument of national policy in their relations with one another
The High Contracting Parties agree that the settlement or solutions of all disputes or conflicts of whatever nature or of whatever origin they may be, which may arise among them, shall never be sought except by pacific means.
The Treaty formed part of the legal basis for the prosecution at the Nuremberg War Crimes trial and led to Principle VI of the Nuremberg Principles, which describes as punishable war crimes a) wars of aggression; b) the ill-treatment of civilians in occupied territory and the wanton destruction of cities, towns and villages; and c) crimes against humanity including inhumane acts done against any civilian population.
For more information see e.g. the Wikipedia artlicle on the Kellog- Briand pact and the full text of the treaty.
The Peace Testimony is probably the best known and best loved of all the Quaker testimonies.... (It) has been a source of inspiration to Friends throughout the centuries, for it points to a way of life which embraces all human relationships.
In 1693 William Penn (the Quaker founder of Pennsylvania) wrote: "A good end cannot sanctify evil means; nor must we ever do evil, that good may come of it... It is as great presumption to send our passions upon God's errands, as it it to palliate them with God's name.... We are too ready to retaliate, rather than forgive, or gain by love and information. And yet we could hurt no man that we believe loves us. Let us then try what Love will do: for if men did once see we love them, we should soon find they would not harm us. Force may subdue, but Love gains: and he that forgives first, wins the laurel."
[From Quaker Faith & Practice 3rd Edition, Chapter 24]