Strategy and tactics, in warfare, related terms referring, respectively, to large-scale and small-scale planning to achieve military success. Strategy may be defined as the general scheme of the conduct of a war, tactics as the planning of means to achieve strategic objectives. Not all theorists of war make this a primary distinction. In the Chinese and Japanese traditions processes and paradoxes are emphasized more than categories. Karl von Clausewitz, the Prussian military theorist, who was influenced by Niccolo Machiavelli, described strategy as the planning of a whole campaign and tactics as the planning of a single battle. In Clausewitz's theory all military strategy is part of the larger political pattern, and all the nation's resources are to be subordinated to the task of attaining the political objective of the war; to this concerted effort he gave the name ?grand strategy.? Antoine H. Jomini, an influential Swiss military theorist and general, regarded strategy as the art of moving forces to the field of battle and tactics as the conduct of forces in battle. Another school views strategy as a means of bringing the enemy to battle and tactics as the means of defeating him in battle. Some theorists focus on clear sets of general principles; some wrote books on principles, formations and maneuvers; and still others dwell on the importance of spirit or other intangibles.

The towering figure in early military science was Alexander the Great, who destroyed the Persian Empire built by Cyrus the Great. He recognized the importance of maintaining reserves, pursuing the enemy, building up supplies (stockpiling), and making use of elaborate scouting (intelligence). In the 4th cent. B.C. Vegetius wrote a summary of military matters which is an important source of information on the Roman military. In the Punic Wars (between Rome and Carthage), Hannibal emerged as the outstanding field commander. His famous victory at Cannae (216 B.C.) over the Roman armies is still studied as an example of battlefield tactics. The study of military theory captured the imagination of several Byzantine emperors, who hoped to restore the glory of the Roman Empire. They studied the operations of the Roman legions and reduced the studies to what may be called the foundations of military science. Strategicon (c.578), compiled by Emperor Maurice, and Tactics (c.900), issued by Emperor Leo VI (Leo the Wise), are exhaustive treatises on the subject.

In Western Europe during the Middle Ages military science did not advance as quickly as its practice did, although siegecraft was much studied. Although early military theorists thought the Crusaders completely ignorant of military principles, recent studies have shown that medieval warfare was not devoid of strategy and tactics. John Zizka, the leader of the Czech Hussites, in the early 15th cent. was particularly innovative. He adopted the wagon-fort as a unit of tactics, made artillery a maneuverable arm, and was the first commander to employ cavalry, infantry, and artillery in efficient tactical combination. He also espoused the principle that mobility is a better protection than armor.

Gustavus Aldolphus (Gustavus II), king of Sweden, and Maurice of Nassau are credited with advancing the professionalization of armies at the end of the 16th cent. By the 17th cent. these professional armies were very costly to establish and maintain, and military strategists employed a cautious approach involving minimal risk of casualties. Even so aggressive a commander as Frederick II (Frederick the Great) was inhibited by fear of a bloody defeat; nevertheless, his wars left Prussia exhausted.

It was Napoleon I who, despite his mistakes, revolutionized the strategy and tactics of his time. Aided by a mass army, he made great use of the powerful shock attack, carefully planned in advance. He also introduced the loose formation, divisional organization, and the use of mobile, long-range artillery. Clausewitz's On War (1832) was an outgrowth of his studies of Napoleonic campaigns; it demonstrated the importance of destroying the enemy on the battlefield and downplayed the importance of the geometrical organization of troops in the field. Jomini's classic Pr?cis de l'art de la guerre (1836), also influenced by a study of Napoleon's campaigns, had a different emphasis. Jomini stressed occupation of enemy territory through carefully planned geometric maneuvers while tactically he emphasized the importance of attacking. His work was influential and was part of the strategy during the U.S. Civil War. The main line of strategic theory, however, followed Clausewitz and culminated in the work of the Prussian-German school of H. K. von Moltke and Alfred von Schlieffen.

The first modern total war, fought with mass armies and modern firearms, was the U.S. Civil War. It demonstrated the importance of industrial mobilization; modern communications (especially railroads and the telegraph), and the deadly effect of new small arms, such as the rifled musket, on mass formations of attacking infantry. Beginning as a contest between armies, it grew into a conflict between two societies; before its termination almost the entire resources of both North and South were engaged.

The lessons of the U.S. Civil War were little noticed in Europe, where strategy and tactics continued to be thought of in terms of mid-19th-century practice. European theorists also ignored the extensive and effective use of machine guns, artillery, and rifles in the colonial wars of the 19th cent. As a result, the bloody stalemate of World War I came as a surprise to most generals. It was characterized by trench warfare and by bloody frontal attacks, which were usually stopped at great cost to the attackers by massed small arms and artillery fire. In an effort to break the stalemate, both sides turned to new technical devices, such as the tank, the airplane, the submarine, and poison gas. The importance of the tank was stressed in theories of mechanized warfare formulated in the 1920s and 30s in the writings of B. H. Liddell Hart, Charles de Gaulle, and J. F. C. Fuller; they proved prophetic when the Nazi blitzkrieg marked World War II as a war of mobility, characterized by vast movements of mechanized armies.

The introduction of aircraft in World War I gave rise to theories of airpower that have dominated strategic and tactical thinking ever since. The basis of airpower was set down by such men as Giulio Douhet, H. M. Trenchard, and William Mitchell, who believed that future wars would be won by air forces. Their theory of strategic bombing called for aerial attacks on the enemy's population and industrial centers to destroy the enemy's will and ability to continue fighting. In World War II that strategy was carried out in massive form by British and U.S. air forces in attacks on Germany and Japan. It was found, however, that aerial bombardment did not cut off industrial production and, in fact, strengthened the enemy's will to continue. In order to win the war the Allies had to conduct a number of campaigns with ground forces and, in the case of Germany, occupy the enemy's homeland.

The introduction and development of nuclear weapons and the guided missile have not changed the basic strategic theory of airpower, but these new weapons have revolutionized airpower itself. The replacement of high-explosive bombs by nuclear bombs and the change from propeller-driven manned aircraft to rocket-powered guided missiles meant that a force armed with these weapons could destroy almost any target on the planet. From the dropping of the first atomic bomb a new school of military theory, nuclear strategy, developed. In the 1950s, the United States evolved the theory of ?massive retaliation,? to be used against the USSR as a response to acts of aggression.

In the early 1960s the threat of nuclear war did not prevent many successful nationalist revolutions and Communist people's wars as advocated by Mao Zedong, Ernesto ?Che? Guevara, and Vo Nguyen Giap. The result was a greater stress on conventional weapons and on increased tactical and strategic flexibility, as well as an interest in the long history and practice of counterinsurgency. That military strategy has become national strategy, involving complex assessments of technological resources, politics, and national priorities, was made clear in the Vietnam War and Afghanistan War where superior strategies and tactics allowed small nations to defeat great powers armed with the latest weaponry.

Outer space has also become a crucial strategic issue. President Ronald Reagan's Strategic Defense Initiative raised the possibility of the use of space-based weapons and satellites to combat an nuclear attack involving ballistic missiles, as the popular term for the program??Star Wars??made clear. Space is also important strategically for intelligence gathering using reconnaissance satellites and for coordination of military forces using the Global Positioning System, as was done successfully during the Persian Gulf War.

Naval strategy and tactics have been shaped by the forms and capabilities of naval warships. Geography is also an important factor in shaping naval thinking. In the Mediterranean, and for islands such as Britain, strong navies were crucial. For the many empires of the Middle East, the Central Asian steppes, or India, naval power was less important or superfluous. Not until Alfred T. Mahan wrote The Influence of Sea Power upon History in the last decade of the 19th cent. was the central theme of naval strategy formulated in universal terms, although the British had been practicing it for hundreds of years. The main strategy of sea power was defined as ?command of the sea,? i.e., the ability to deny use of the sea as a means of transportation to an enemy while simultaneously protecting one's own merchant shipping, and the ability to use the sea to project power ashore while denying that capability to the enemy. Despite the introduction of new weapons such as steam warships, armored ships, heavy ordnance, submarines, and aircraft, ?command of the sea? remained a fundamental objective of naval strategy. Another important naval strategy is ?overseas presence,? i.e., the visible display of seapower as a deterrent to intervention by opposing powers in key areas of international tension.

The development of airpower has led to a host of changes, including the emergence of aircraft carriers and naval air fleets and the development of submarine-based retaliatory missile forces. The employment of land-based and carrier-based aircraft during World War II showed that command of the seas rested in great part on control of the air above it. The submarine, introduced in World War I, greatly changed naval strategy and led to the development of many new weapons and tactics. In both world wars the submarine was employed mainly as a commerce destroyer and, as such, could not by itself gain command of the sea. However, the use of long-range guided missiles on nuclear-powered submarines in the 1960s transformed the submarine into a major weapon of strategic bombardment. Nuclear-powered submarines carrying guided missiles are almost invulnerable to attack.