“History teaches, perhaps, very few clear lessons. But surely one such lesson learned by the world at great cost is that aggression, unopposed, becomes a contagious disease.”

Source: Deadhouse Gates

Robert Rosen (2013), Essays on Life Itself Chapter 18

Source: Joseph Anton: A Memoir

Counterterrorism and Cybersecurity: Total Information Awareness (2nd Edition), 2015

Letter to Professor Demmon (16 December 1871), in The Life and Public Services of James A. Garfield (1881) by E. E. Brown, p. 424 http://books.google.com/books?id=vCAFAAAAYAAJ <br class="br">1870s

Introduction, as translated by H. B. Nisbet (1975)
Variant translation: What experience and history teach is this — that people and governments never have learned anything from history, or acted on principles deduced from it.
Pragmatical (didactic) reflections, though in their nature decidedly abstract, are truly and indefeasibly of the Present, and quicken the annals of the dead Past with the life of to-day. Whether, indeed, such reflections are truly interesting and enlivening, depends on the writer's own spirit. Moral reflections must here be specially noticed, the moral teaching expected from history; which latter has not unfrequently been treated with a direct view to the former. It may be allowed that examples of virtue elevate the soul, and are applicable in the moral instruction of children for impressing excellence upon their minds. But the destinies of peoples and states, their interests, relations, and the complicated tissue of their affairs, present quite another field. Rulers, Statesmen, Nations, are wont to be emphatically commended to the teaching which experience offers in history. But what experience and history teach is this, that peoples and governments never have learned anything from history, or acted on principles deduced from it. Each period is involved in such peculiar circumstances, exhibits a condition of things so strictly idiosyncratic, that its conduct must be regulated by considerations connected with itself, and itself alone. Amid the pressure of great events, a general principle gives no help. It is useless to revert to similar circumstances in the Past. The pallid shades of memory struggle in vain with the life and freedom of the Present.
Lectures on the History of History Vol 1 p. 6 John Sibree translation (1857), 1914
Lectures on the Philosophy of History (1832), Volume 1

1962, Cuban Missile Crisis speech

Source: Go Set a Watchman