Since the earliest days of warfare, military operations have followed a predictable formula: after a decisive battle, an army must pursue the enemy and destroy its organization in order to achieve a victorious campaign. But by the mid-19th century, the emergence of massive armies and advanced weaponry - and the concomitant decline in the effectiveness of cavalry - had diminished the practicality of pursuit, producing campaigns that bogged down short of decisive victory. Great battles had become curiously indecisive, decisive campaigns virtually impossible.