John Lancaster is a British journalist.

There are years whose impact on human history is apparent to everyone at the time—1776, say, or 1945, or 2001—and then there are years whose significance seems to grow in retrospect, as it becomes clear that the consequences of certain events are still being felt decades later. Everyone who was an adult in 1989 knew straight away that the fall of the Berlin Wall was a momentous event. What, though, if those events were contingent on things that had happened in another, even more momentous year? Christian Caryl’s book “Strange Rebels: 1979 and the Birth of the 21st Century” (Basic) asks the question, What if the really important year in recent history was 1979?

At the start of 1978, the biggest country in the world, the Soviet Union, and the most populous country in the world, China, both seemed immovable monoliths of Communist ideology. Iran was run by the Shah, and the aging leader of the clerical opposition, Ayatollah Khomeini, was in exile in Iraq. Afghanistan was under the control of Mohammad Daoud, a French-educated secularist, keen on modernization and women’s rights, and the main threat to his autocratic rule came from a different flavor of secularist, those of the People’s Democratic Party of Afghanistan, who were Communists. The Iron Curtain seemed a permanent division between the free and the unfree, and the Cold War was the dominant fact of global politics....