Fifth column refers to undercover agents operating within the ranks of an enemy to undermine its cause. The agents pave the way for military or political invasion. They may work in an army, political party, or industry. Their activities include spying, sabotage, economic subversion, propaganda, agitation, infiltration, and even assassination, terror, and revolt. The term fifth column was first used during the Spanish Civil War (1936-1939) to describe the work of Francisco Franco’s followers in Loyalist Madrid. Emilio Mola, a general under Franco, said, “I have four columns moving against Madrid, and a fifth will rise up inside the city itself.”
