A frequent theme of Wells's work, as in his 1901 nonfiction book Anticipations, was the history of humans' mastery of power and energy through technological advance, seen as a determinant of human progress. The novel begins: "The history of mankind is the history of the attainment of external power. Man is the tool-using, fire-making animal. . . . Always down a lengthening record, save for a set-back ever and again, he is doing more."(Many of the ideas Wells develops here found a fuller development when he wrote The Outline of History in 1918-1919.)