Generally, a battle is a conceptual component in the hierarchy of combat in warfare between two or more armed forces, wherein each group will seek to defeat the others within the scope of a military campaign, and are well defined in duration, area and force commitment. Wars and military campaigns are guided by strategy, whereas battles take place on a level of planning and execution known as operational warfare. German strategist Carl von Clausewitz stated that "the employment of battles . . . to achieve the object of war was the essence of strategy.
The defining characteristics of the battle as a concept in the Theory of combat has been a dynamic one through the course of military history, changing with the changes in the organisation, employment and technology of military forces.
While the British military historian Sir John Keegan suggested an ideal definition of battle as "something which happens between two armies leading to the moral then physical disintegration of one or the other of them the origins and outcomes of battles can rarely be summarized so neatly.
In general a battle during the 20th century was, and continues to be defined by the combat between opposing forces representing major components of total forces committed to the military campaign, used to achieve a specific military objectives, within a time-frame of less than a month. Where the duration of the battle is longer then a week, they are often for reasons of staff operational planning called operations. Battles can be planned, encountered, or forced by one force on the other when it is unable to withdraw from combat.
The a battle always has as its purpose the reaching of a mission goal by use of military force. A victory in the battle is achieved when one of the opposing sides forces the other to abandon its mission, or is forced to surrender its forces, have its forces rout, forced to retreat or rendered militarily ineffective for further combat operations. However, a battle may end in a Pyrrhic victory which ultimately favors the defeated party. If no resolution is reached in battle, it can result is a stalemate. A conflict in which one side is unwilling to reach a decision by a direct battle using conventional military forces often becomes an insurgency.
Up until the 19th century the majority of battles were of short duration, many lasting a part of a day or less, the Battle of Nations (1813) and the Battle of Gettysburg (1863) were exceptional for lasting three days. This was mainly due to the difficulty of supplying armies in the field, or conducting night operations. Typically, the means of prolonging a battle was by employment of siege warfare. Improvements in transportation, and the sudden evolving of trench warfare with its siege-like nature during the First World War in the 20th century, lengthened the duration of battles to days and weeks. This created the requirement for unit rotation to prevent combat fatigue, with troops preferably not remaining in combat area of operations for more than a month. This theory proved to be completely unmanageable during the Second World War.
The use of the term "battle" in military history has led to its misuse when referring to almost any scale of combat, notably by strategic forces involving hundreds of thousands of troops that may be engaged in either a single battle at one time (Battle of Leipzig) or multiple operations (Battle of Kursk). The space a battle occupies depends on the range of the weapons of the combatants, and may occupy large geographic areas as in the case of the Battle of Britain or the Battle of the Atlantic. Until the advent of artillery and aircraft, battles were fought with the two sides in sight, if not reach, of each other. The depth of the battlefield has also increased in modern warfare with inclusion of the supporting units in the rear areas; supply, artillery, medical, etc.; now outnumbering the front-line combat troops.
Battles are, on the whole, made up of a multitude of individual combats, skirmishes and small engagements within the context of which the combatants will usually only experience a small part of the events of the battle's entirety. To the infantryman, there may be little to distinguish between combat as part of a minor raid or a major offensive, nor is it likely that they anticipate the future course of the battle; few of the British infantry who went over the top on the first day on the Somme, 1 July, 1916, would have anticipated that they would be fighting the same battle in five months time. Conversely, some of the Allied infantry who had just dealt a crushing defeat to the French at the Battle of Waterloo fully expected to have to fight again the next day.
Battles can be fought on land, sea and in the modern age, in the air. Naval battles have occurred since before the 5th century BC. Air battles have been far less common, due to its late conception, the most prominent being the Battle of Britain in 1940. However since the Second World War land or sea battles have come to rely on air support. Indeed, during the Battle of Midway, five aircraft carriers were sunk without either fleet coming into direct contact.
There are numerous types of battle. A "battle of encounter" is a meeting engagement where the opposing sides collide in the field without either having prepared their attack or defence. The goal of a "battle of attrition" is to inflict greater loss on the enemy than you suffer yourself; many battles of the Western Front in the First World War were intentionally (Verdun) or unintentionally (Somme) attrition battles. A "battle of breakthrough" aims to pierce the enemy's defences, thereby exposing the vulnerable flanks which can be turned. A "battle of encirclement"—the Kesselschlacht of the German Blitzkrieg—surrounds the enemy in a pocket. A "battle of envelopment" involves an attack on one or both flanks; the classic example being the double-envelopment of the Battle of Cannae. A "battle of annihilation" is one in which the defeated party is destroyed in the field, such as the French fleet at the Battle of the Nile.
A "decisive battle" is one of particular importance; often by bringing hostilities to an end, such as the Battle of Hastings or the Battle of Hattin, or as a turning point in the fortunes of the belligerents, such as the Battle of Stalingrad. A decisive battle can have political as well as military impact, changing the balance of power or boundaries between countries. The concept of the "decisive battle" became popular with the publication in 1851 of Edward Creasy's The Fifteen Decisive Battles of the World. British military historians J.F.C. Fuller (The Decisive Battles of the Western World) and B.H. Liddell Hart (Decisive Wars of History), among many others, have written books in the style of Creasy's work.
Another important use of aircraft came with the development of the helicopter, which first became heavily used during the Vietnam War, and still continues to be widely used today to transport and augment ground forces.
Today, direct engagements between aircraft are rare - the most modern fighter-interceptors carry much more extensive bombing payloads, and are used to bomb precision land targets, rather than to fight other aircraft. Anti-aircraft batteries are used much more extensively to defend against incoming aircraft than interceptors. Despite this, aircraft today are much more extensively used as the primary tools for both army and navy, as evidenced by the prominent use of helicopters to transport and support troops, the use of aerial bombardment as the "first strike" in many engagements, and the replacement of the battleship with the aircraft carrier as the center of most modern navies.
Battles are almost invariably named after some feature of the battlefield geography, such as the name of a town, forest or river. Occasionally battles are named after the date on which they took place, such as The Glorious First of June. In the Middle Ages it was considered important to settle on a suitable name for a battle which could be used by the chroniclers. For example, after Henry V of England defeated a French army on 25 October, 1415, he met with the senior French herald and they agreed to name the battle after the nearby castle and so it was called the Battle of Agincourt. In other cases, the sides adopted different names for the same battle, such as the Battle of Gallipoli which is known in Turkey as the Battle of Çanakkale. Sometimes in desert warfare, there is no nearby town name to use; map coordinates gave the name to the Battle of 73 Easting in the First Gulf War.
Some place names have become synonymous with the battles that took place there, such as the Passchendaele, Pearl Harbor, the Alamo or Waterloo. Military operations, many of which result in battle, are given codenames, which are not necessarily meaningful or indicative of the type or the location of the battle. Operation Market Garden and Operation Rolling Thunder are examples of battles known by their military codenames.
When a battleground is the site of more than one battle in the same conflict, the instances are distinguished by ordinal number, such as the First and Second Battles of Bull Run. An extreme case are the twelve Battles of the Isonzo—First to Twelfth—between Italy and Austria-Hungary during the First World War.
Some battles are named for the convenience of military historians so that periods of combat can be neatly distinguished from one another. Following the First World War, the British Battles Nomenclature Committee was formed to decide on standard names for all battles and subsidiary actions. To the soldiers who did the fighting, the distinction was usually academic; a soldier fighting at Beaumont Hamel on 13 November 1916 was probably unaware he was taking part in what the committee would call the "Battle of the Ancre".
Many combats are too small to merit a name. Terms such as "action", "skirmish", "firefight", "raid" or "offensive patrol" are used to describe small-scale battle-like encounters. These combats often take place within the time and space of a battle and while they may have an objective, they are not necessarily "decisive". Sometimes the soldiers are unable to immediately gauge the significance of the combat; in the aftermath of the Battle of Waterloo, some British officers were in doubt as to whether the day's events merited the title of "battle" or would be passed off as merely an "action".
Battles also affect politics. A decisive battle can cause the losing side to surrender, while a Pyrrhic Victory such as the Battle of Isandlwana can cause the winning side to reconsider its long-term goals. Battles in civil wars have often decided the fate of monarchs or political factions. Famous examples include the War of the Roses, as well as the Jacobite Uprisings. Battles also affect the commitment of one side or the other to the continuance of a war, for example the Battle of Incheon and the Battle of Hue during the Tet Offensive.