“A great civilization is not conquered from without until it has destroyed itself from within.”

“A great civilization is not conquered from without until it has destroyed itself from within.”

“The conservative who resists change is as valuable as the radical who proposes it.”

“Education is the transmission of civilization.”

“A great civilization is not conquered from without until it has destroyed itself from within.”

“History is, above all else, the creation and recording of that heritage; progress is its increasing abundance, preservation, transmission, and use. To those of us who study history not merely as a warning reminder of man's follies and crimes, but also as an encouraging remembrance of generative souls, the past ceases to be a depressing chamber of horrors; it becomes a celestial city, a spacious country of the mind, wherein a thousand saints, statesmen, inventors, scientists, poets, artists, musicians, lovers, and philosophers still live and speak, teach and carve and sing.”

“We may make contact with ambitious species on other planets or stars; soon thereafter there will be interplanetary war. Then, and only then, will we of this earth be one.”