“Every civilization that has ever existed has ultimately collapsed … History is a tale of efforts that failed, of aspirations that weren’t realized... So, as a historian, one has to live with a sense of the inevitability of tragedy.”

Source: The Drunkard's Walk, Chapter 10, The Drunkard's Walk, p. 201

My Disillusionment in Russia (1923)

is equally relevant.
The World's Last Night (1952)

Source: War and peace (2005), p. 1

The Reappearance of the Christ and the Masters of Wisdom (1980)

Paraphrased from a letter C. S. Lewis wrote to Mrs. Johnson on March 16, 1955: "A housewife's work [is] surely, in reality, the most important work in the world ... your job is the one for which all others exist", as reported in The Misquotable C.S. Lewis (2018) by William O'Flaherty, p. 63
Misattributed

As quoted in Lasker's Chess Magazine
About

1961, UN speech
Context: Terror is not a new weapon. Throughout history it has been used by those who could not prevail, either by persuasion or example. But inevitably they fail, either because men are not afraid to die for a life worth living, or because the terrorists themselves came to realize that free men cannot be frightened by threats, and that aggression would meet its own response. And it is in the light of that history that every nation today should know, be he friend or foe, that the United States has both the will and the weapons to join free men in standing up to their responsibilities.