Military strategy
Fundamentals: Military strategy is the planning and execution of the contest between groups of armed adversaries. It is a subdiscipline of warfare and of foreign policy, and a principal tool to secure national interests. Its perspective is larger than military tactics, which involve the disposition and manoeuvre of units on a particular sea or battlefield, but less broad than grand strategy otherwise called national strategy, which is the overarching strategy of the largest of organizations such as the nation state, confederation, or international alliance and involves using diplomatic, informational, military and economic resources. Military strategy involves using military resources such as people, equipment, and information against the opponent's resources to gain supremacy or reduce the opponent's will to fight, developed through the precepts of military science.
NATO's definition of strategy is "presenting the manner in which military power should be developed and applied to achieve national objectives or those of a group of nations." Strategy may be divided into 'grand strategy', geopolitical in scope and 'military strategy' that converts the geopolitical policy objectives into militarily achievable goals and campaigns. Field Marshal Viscount Alanbrooke, Chief of the Imperial General Staff and co-chairman of the Anglo-US Combined Chiefs of Staff Committee for most of the Second World War, described the art of military strategy as: "to derive from the [policy] aim a series of military objectives to be achieved: to assess these objectives as to the military requirements they create, and the pre-conditions which the achievement of each is likely to necessitate: to measure available and potential resources against the requirements and to chart from this process a coherent pattern of priorities and a rational course of action." Field-Marshal Montgomery summed it up thus "Strategy is the art of distributing and applying military means, such as armed forces and supplies, to fulfil the ends of policy. Tactics means the dispositions for, and control of, military forces and techniques in actual fighting. Put more shortly: strategy is the art of the conduct of war, tactics the art of fighting."

Background: Military strategy in the 19th century was still viewed as one of a trivium of "arts" or "sciences" that govern the conduct of warfare; the others being tactics, the execution of plans and maneuvering of forces in battle, and logistics, the maintenance of an army. The view had prevailed since the Roman times, and the borderline between strategy and tactics at this time was blurred, and sometimes categorization of a decision is a matter of almost personal opinion. Carnot, during the French Revolutionary Wars thought it simply involved concentration of troops.
Strategy and tactics are closely related and exist on the same continuum; modern thinking places the operational level between them. All deal with distance, time and force but strategy is large scale, can endure through years, and is societal while tactics are small scale and involve the disposition of fewer elements enduring hours to weeks. Originally strategy was understood to govern the prelude to a battle while tactics controlled its execution. However, in the world wars of the 20th century, the distinction between maneuver and battle, strategy and tactics, expanded with the capacity of technology and transit. Tactics that were once the province of a company of cavalry would be applied to a panzer army.
It is often said that the art of strategies defines the goals to achieve in a military campaign, while tactics defines the methods to achieve these goals. Strategic goals could be "We want to conquer area X", or "We want to stop country Y's expansion in world trade in commodity Z"; while tactical decisions range from a general statement—e.g., "We're going to do this by a naval invasion of the North of country X", "We're going to blockade the ports of country Y", to a more specific "C Platoon will attack while D platoon provides fire cover".
In its purest form, strategy dealt solely with military issues. In earlier societies, a king or political leader was often the same person as the military leader. If not, the distance of communication between the political and the military leader was small. But as the need of a professional army grew, the bounds between the politicians and the military came to be recognized. In many cases, it was decided that there was a need for a separation.
As French statesman Georges Clemenceau said, "War is too important a business to be left to soldiers." This gave rise to the concept of the grand strategy which encompasses the management of the resources of an entire nation in the conduct of warfare. In the environment of the grand strategy, the military component is largely reduced to operational strategy—the planning and control of large military units such as corps and divisions. As the size and number of the armies grew and the technology to communicate and control improved, the difference between "military strategy" and "grand strategy" shrank. Fundamental to grand strategy is the diplomacy through which a nation might forge alliances or pressure another nation into compliance, thereby achieving victory without resorting to combat. Another element of grand strategy is the management of the post-war peace.
As Clausewitz stated, a successful military strategy may be a means to an end, but it is not an end in itself. There are numerous examples in history where victory on the battlefield has not translated into goals such as long term peace, security or tranquillity.

Principles: Many military strategists have attempted to encapsulate a successful strategy in a set of principles. Sun Tzu defined 13 principles in his The Art of War while Napoleon listed 115 maxims. American Civil War General Nathan Bedford Forrest had only one: to "[get] there first with the most men". The concepts given as essential in the United States Army Field Manual of Military Operations (FM 3–0) are:

Objective type (direct every military operation towards a clearly defined, decisive, and attainable objective)
Offensive type (seize, retain, and exploit the initiative)
Mass Type (concentrate combat power at the decisive place and time)
Economy of force type (allocate minimum essential combat power to secondary efforts)
Maneuver type (place the enemy in a disadvantageous position through the flexible application of combat power)
Unity of command type (for every objective, ensure unity of effort under one responsible commander)
Security type (never permit the enemy to acquire an unexpected advantage)
Surprise type (strike the enemy at a time, at a place, or in a manner for which they are unprepared)
Simplicity type (prepare clear, uncomplicated plans and clear, concise orders to ensure thorough understanding)
According to Greene and Armstrong, some planners assert adhering to the fundamental principles guarantees victory, while others claim war is unpredictable and the strategist must be flexible. Others argue predictability could be increased if the protagonists were to view the situation from the other sides in a conflict. Field Marshal Count Helmuth von Moltke expressed strategy as a system of "ad hoc expedients" by which a general must take action while under pressure. These underlying principles of strategy have survived relatively unchanged as the technology of warfare has developed.
Strategy (and tactics) must constantly evolve in response to technological advances. A successful strategy from one era tends to remain in favor long after new developments in military weaponry and matériel have rendered it obsolete. World War I, and to a great extent the American Civil War, saw Napoleonic tactics of "offense at all costs" pitted against the defensive power of the trench, machine gun and barbed wire. As a reaction to its World War I experience, France attempted to use its Maginot Line to apply the principles of mass and economy of force, in that troops could be concentrated in the north for an offensive there while the Line acted as force multiplier in the south, and maneuver and security, by preventing the Germans from going directly from Alsace to Paris.

Development: 

Antiquity: The principles of military strategy emerged at least as far back as 500 BC in the works of Sun Tzu and Chanakya. The campaigns of Alexander the Great, Chandragupta Maurya, Hannibal, Qin Shi Huang, Julius Caesar, Zhuge Liang, Khalid ibn al-Walid and, in particular, Cyrus the Great demonstrate strategic planning and movement. Mahan describes in the preface to The Influence of Sea Power upon History how the Romans used their sea power to effectively block the sea lines of communication of Hannibal with Carthage; and so via a maritime strategy achieved Hannibal's removal from Italy, despite never beating him there with their legions.
One of these strategies was shown in the battle between Greek city states and Persia. The Battle of Thermopylae in which the Greek forces were outnumbered stood as a good military strategy. The Greek allied forces ultimately lost the battle, but the training, use of armor, and location allowed them to defeat many Persian troops before losing. In the end, the Greek alliance lost the battle but not the war as a result of that strategy which continued on to the battle of Plataea. The Battle of Plataea in 479 BC resulted in a victory for the Greeks against Persia, which exemplified that military strategy was extremely beneficial to defeating a numerous enemy.
Early strategies included the strategy of annihilation, exhaustion, attrition warfare, scorched earth action, blockade, guerrilla campaign, deception and feint. Ingenuity and adeptness were limited only by imagination, accord, and technology. Strategists continually exploited ever-advancing technology.