Fifth Column

Term that refers to any clandestine group or faction of subversive agents who attempt to undermine a nation's solidarity from inside its own borders. A fifth column is a group of secret sympathizers or enemy supporters that engage in espionage or sabotage within national borders.

Soviet revolutionary leader Leon Trotsky originally used the term fifth column to describe his Fifth Army, an elite military unit that operated during the Russian Civil War. But it is Emilio Mola Vidal, a Nationalist general during the 1930s Spanish Civil War, who is generally credited with coining the term. Mola's army, which comprised four columns, moved on Madrid. As they did so, the general referred to his militant supporters within the capital as his fifth column, intent on undermining the loyalist government from within. The term itself was popularized by writers such as Ernest Hemingway, who used the term in his book The Fifth Column and Four Stories of the Spanish Civil War.

During the Cold War, communist sympathizers in the United States were frequently termed a “fifth column.” More recent conflicts have had their own fifth columns. These include Cuban rebels during the Bay of Pigs invasion and Iraqi insurgents in the aftermath of the Iraq War of 2003. The term has also been extended to a number of modern U.S. domestic issues—for example, in the debate over abortion, it has been argued that the “right-to-life” movement has established a fifth column among freedom-of-choice advocates.