"The Great Illusion" argued that economic integration made war unlikely. He was wrong in that he hadn't realized how much people wanted something that went against their interests.

But he learned that lesson well: "From the mid-1930s, Angell actively campaigned for collective international opposition to the aggressive policies of Germany, Italy, and Japan. He went to the United States in 1940 to lecture in favour of American support for Britain in World War II"[1]

[1] https://en.wikipedia.org/wiki/Norman_Angell