Over the past year, workers at Google, Microsoft and Amazon have demanded that their employers stop supplying technology to the U.S. military and other government agencies. But a new book from the historian Margaret O’Mara shows how the tech industry might not exist without the patronage of big government—and particularly the defense industry.   

Ms. O’Mara’s book—“The Code: Silicon Valley and the Remaking of America”—is an exhaustive chronicle that spans the Valley’s Cold War origins through the tech backlash that accelerated after the presidential election of 2016. The most eye-opening part of the book is its early chapters on the military funding that poured into research and development projects at Stanford and the early companies that cropped up on the sunny flats of the peninsula south of San Francisco.