It was March 21, 2003—two days after the United States began its “shock and awe” campaign against Iraq—and the story dominating TV networks was the rumor (later proven false) that Saddam Hussein’s infamous cousin, Ali Hassan al-Majid (“Chemical Ali”), had been killed in an airstrike. But, for thousands of other people around the world who switched on their computers rather than their television sets, the lead story was the sudden and worrisome disappearance of Salam Pax.

Otherwise known as the “Baghdad Blogger,” Salam Pax was the pseudonym for a 29-year-old Iraqi architect whose online diary, featuring wry and candid observations about life in wartime, transformed him into a cult figure. It turned out that technical difficulties, not U.S. cruise missiles or Baathist Party thugs, were responsible for the three-day Salam Pax blackout. In the months that followed, his readership grew to millions, as his accounts were quoted in the New York Times, BBC, and Britain’s Guardian newspaper. If the first Gulf War introduced the world to the “CNN effect,” then the second Gulf War was blogging’s coming out party. Salam Pax was the most famous blogger during that conflict (he later signed a book and movie deal), but myriad other online diarists, including U.S. military personnel, emerged to offer real-time analysis and commentary.

Blogs (short for “weblogs”) are periodically updated journals, providing online commentary with minimal or no external editing. They are usually presented as a set of “posts,” individual entries of news or commentary, in reverse chronological order. The posts often include hyperlinks to other ...