"One might also ask whether war can be justified from the Christian ethical perspective when one starts the war oneself. This question, however, leads back to a broader problem, to the question of the relation between history and God, people and God, growth and God. Peoples [Völker] are like individuals. At first they are immature and need guidance. Then they grow into the blossom of youth, mature into adults, and die. This situation is neither good nor bad in and of itself, yet profound questions are concealed here. For growth involves expansion; an increase in strength involves pushing aside other individuals. In that respect the life of an individual person is no different than that of a people. Every people, however, has within itself a call from God to create its history, to enter into the struggle that is the life of nations. This call must be heeded amid the growth and development so that it takes place before the face of God. God calls a people to diversity, to struggle, to victory. Strength also comes from God, and power, and victory, for God creates youth in the individual as well as in nations, and God loves youth, for God himself is eternally young and strong and victorious. And fear and weakness will be conquered by courage and strength. Now, should a people experiencing God’s call in its own life, in its own youth, and in its own strength, should not such a people also be allowed to follow that call even if it disregards the lives of other peoples? God is the Lord of history; and if a people bends in humility to this holy will guiding history, then with God in its youth and strength it can overcome the weak and disheartened. Then God will be with it. The determination as to when this moment has arrived for a people can and may only be made by human beings who are conscious of the grave responsibility for what they do, surrendering their own selfish will to the divine will that guides world history." ("Basic Questions of a Christian Ethic", 1929.)Detta sätt att argumentera hade länge varit standard inom tysk teologi (och tysk akademi i allmänhet) och levde vidare efter första världskriget Få ifrågasatte det. Schweizaren Barth, vid denna tid professor i Tyskland, var en av få. Man såg det inte som en etisk fråga. Sådan är världen. Att ifrågasätta expansionskrig vore att ifrågasätta Tyskland och andra nationers legitimitet.
Vid samma tid är fredsrörelsen och även pacifism mycket stark i amerikansk kristenhet. Det är under Bonhoeffers tid i New York 1930/31, bl a i mötet med sin medstudent fransmannen Jean Lasserre och sitt möte med en svart baptistkyrka där han är aktiv, han blir pacifist och ändrar sin syn på kyrka och kristen etik i allmänhet.