It is an expression used during the Vietnam War by the Americans as a euphemism for "civilian casualties or material losses resulting from military action that did not target them." He became popular during the Persian Gulf War, for his repetition in newspaper reports. Today it extends to any harm caused by an action that was directed to another end, especially if contempt for harm to innocents is obvious. It comes from the English collateral damage , and it is because collateral ( "next, next to" ) has for that language a meaning of "secondary, consequence of the main".