“My dear Professor, a war would have cost us at least 30,000 brave soldiers, and at best we should have gained nothing by it. Besides, anyone who has once looked into the glassy eyes of a dying warrior on the battle-field would think twice before beginning a war.”
Mein lieber Professor, ein solcher Krieg hätte uns wenigstens 30,000 Mann brave Soldaten gekostet, und uns im besten Falle keinen Gewinn gebracht. Wer aber nur ein Mal in das brechende Auge eines sterbenden Kriegers auf dem Schlachtfeld geblickt hat, der besinnt sich, bevor er einen Krieg anfängt.
In June 1867, protecting the Treaty of London
1860s
Original
Mein lieber Professor, ein solcher Krieg hätte uns wenigstens 30,000 Mann brave Soldaten gekostet, und uns im besten Falle keinen Gewinn gebracht. Wer aber nur ein Mal in das brechende Auge eines sterbenden Kriegers auf dem Schlachtfeld geblickt hat, der besinnt sich, bevor er einen Krieg anfängt.
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Otto von Bismarck 35
German statesman, Chancellor of Germany 1815–1898Related quotes

Hope, Despair, and Memory (1986)

“Anyone who thinks must think of the next war as they would of suicide.”
Source: Eleanor and Franklin
Source: Lenovo Group’s Liu Chuanzhi on ‘Building a Healthy Company’ https://knowledge.wharton.upenn.edu/article/lenovo-groups-liu-chuanzhi-on-building-a-healthy-company/ in Knowledge @ Wharton (8 July 2009)

Conclusion
1880s, Personal Memoirs of General U. S. Grant (1885)

"President Truman Did Not Understand" http://www.peak.org/~danneng/decision/usnews.html in U.S. News & World Report (15 August 1960)
Variant: If the Germans had dropped atomic bombs on cities instead of us, we would have defined the dropping of atomic bombs on cities as a war crime, and we would have sentenced the Germans who were guilty of this crime to death at Nuremberg and hanged them.
As quoted in The Decision to Drop the Atomic Bomb (1996) by Dennis Wainstock, p. 122
Context: Suppose Germany had developed two bombs before we had any bombs. And suppose Germany had dropped one bomb, say, on Rochester and the other on Buffalo, and then having run out of bombs she would have lost the war. Can anyone doubt that we would then have defined the dropping of atomic bombs on cities as a war crime, and that we would have sentenced the Germans who were guilty of this crime to death at Nuremberg and hanged them?
But, again, don't misunderstand me. The only conclusion we can draw is that governments acting in a crisis are guided by questions of expediency, and moral considerations are given very little weight, and that America is no different from any other nation in this respect.