In her instructions to Harvard’s young historians, called ‘How to Write a Paper for This Class’, Professor Jill Lepore advises, ‘Every argument worth making begins with a question.’ The question that runs through her riveting account of the developing links, in the second half of the last century, between computing technology and politics is ‘What if?’ Now, as Lepore points out right at the start, ‘History cannot answer “What if?” but it can explain what happened, and why.’ And yet this is the question that the creators of the Simulmatics Corporation sought, in any number of different political contexts, to get computers to answer.

Her book is built around the history of this company and the men – for they were all men – who created and ran it. Launched in 1959, Simulmatics went bust in 1970. Why should one of America’s most distinguished academic historians devote almost