The term small wars was used by British and, later, American military thinkers to distinguish warfare against guerrilla forces and tribal armies from the major conventional style of war that characterized warfare on the European continent. The Marine Corps Small Wars Manual published in 1940 recognized that the phrase was "often a vague name for any one of a great variety of military operations." By comparison to small wars, "doctrine" is a more slippery concept to define. Making the distinction between formal and informal types of doctrine can be useful in two ways. First, folding informal doctrine into the overall analysis of doctrine formation helps explain the lag that may arise between prosecuting relatively new ways of war and developing doctrine for passing on the lessons of those new ways. Second, it contributes to an understanding of the role individuals play in the development of doctrine, particularly formal doctrine.