“What really matters is that we should all of us realize that we are guilty of inhumanity. The horror of this realization should shake us out of our lethargy so that we can direct our hopes and our intentions to the coming of an era in which war will have no place.”

Letter to his eldest son, Frank Joslyn Baum (September 1918)
Letters and essays

Source: Propaganda (1928), p.59

Putin's war of smoke and mirrors (2016)

The Basic Teachings - Part 1: Principles of the Teaching (2009)

David C. McClelland (1978). "Managing motivation to expand human freedom". American Psychologist. 33 (3): 201

The Problem of Peace (1954)
Context: We have learned to tolerate the facts of war: that men are killed en masse — some twenty million in the Second World War — that whole cities and their inhabitants are annihilated by the atomic bomb, that men are turned into living torches by incendiary bombs. We learn of these things from the radio or newspapers and we judge them according to whether they signify success for the group of peoples to which we belong, or for our enemies. When we do admit to ourselves that such acts are the results of inhuman conduct, our admission is accompanied by the thought that the very fact of war itself leaves us no option but to accept them. In resigning ourselves to our fate without a struggle, we are guilty of inhumanity.

Preface to the first edition, 1865
The Ethics of the Dust (1875)

Letter to http://memory.loc.gov/cgi-bin/query/r?ammem/mtj:@field(DOCID+@lit(tj110158)) Thomas Leiper (12 June 1815). Published in The Works of Thomas Jefferson in Twelve Volumes http://oll.libertyfund.org/ToC/0054.php, Federal Edition, Paul Leicester Ford, ed., New York: G. P. Putnam's Sons, 1904, Vol. 11 http://oll.libertyfund.org/Texts/Jefferson0136/Works/0054-11_Bk.pdf, pp. 477–478.
The sentence "I hope our wisdom will grow with our power, and teach us, that the less we use our power, the greater it will be." was used by US-President Barack Obama in his A New Beginning Speech.
1810s
Context: We concur in considering the government of England as totally without morality, insolent beyond bearing, inflated with vanity and ambition, aiming at the exclusive dominion of the sea, lost in corruption, of deep-rooted hatred towards us, hostile to liberty wherever it endeavors to show its head, and the eternal disturber of the peace of the world. In our estimate of Bonaparte, I suspect we differ. [... ] Our form of government is odious to him, as a standing contrast between republican and despotic rule; and as much from that hatred, as from ignorance in political economy, he had excluded intercourse between us and his people, by prohibiting the only articles they wanted from us, that is, cotton and tobacco. Whether the war we have had with England, and the achievements of that war, and the hope that we may become his instruments and partisans against that enemy, may induce him, in future, to tolerate our commercial intercourse with his people, is still to be seen. For my part, I wish that all nations may recover and retain their independence; that those which are overgrown may not advance beyond safe measures of power, that a salutary balance may be ever maintained among nations, and that our peace, commerce, and friendship, may be sought and cultivated by all. It is our business to manufacture for ourselves whatever we can, to keep our markets open for what we can spare or want; and the less we have to do with the amities or enmities of Europe, the better. Not in our day, but at no distant one, we may shake a rod over the heads of all, which may make the stoutest of them tremble. But I hope our wisdom will grow with our power, and teach us, that the less we use our power, the greater it will be.

Source: The Image: A Guide to Pseudo-Events in America (1961), p. 261.