ONE OF the most enduring mysteries of the final years of the Cold War was a period of great tension and worry about nuclear conflict between the United States and Soviet Union. The “war scare” of 1983, which unfolded 30 years ago this month, is still shrouded in unknowns, but new information has come to light lately, and the events are relevant and worth pondering today.

In March of that year, President Ronald Reagan called the Soviet Union an “evil empire.” Soon after, he announced the Strategic Defense Initiative, his “Star Wars” quest for a defense against ballistic missiles carrying nuclear warheads. In the summer, the United States carried out a provocative Pacific Ocean naval exercise aimed at the Soviet Union. On Sept. 1, the Soviets mistakenly shot down a Korean airliner, killing all 269 people aboard. In October, Reagan had a detailed briefing on U.S. plans for nuclear war. In November, the ABC made-for-television film, “The Day After,” depicting a fictional nuclear attack on Lawrence, Kan., drew what was then the second-largest audience in history for a single television program. Reagan wrote in his diary that the film left him “greatly depressed.”...