“Lo que la experiencia y la historia enseñan es que los pueblos y los gobiernos jamás han aprendido algo de la historia ni han actuado según las lecciones que hubieran tenido que sacarse de ella.”

Original

What experience and history teach is this — that nations and governments have never learned anything from history, or acted upon any lessons they might have drawn from it.

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