Theater – operation over a large, often continental area of operation and represents a strategic national commitment to the conflict such as Operation Barbarossa, with general goals that encompass areas of consideration outside of the military such as the economic and political impacts.
Campaign – subset of the theatre operation, or a more limited geographic and operational strategic commitment such as Battle of Britain, and need not represent total national commitment to a conflict, or have broader goals outside of the military impacts.
Battle – subset of a campaign that will have specific military goals and geographic objectives, as well as clearly defined use of forces such as the Battle of Gallipoli, which operationally was a combined arms operation originally known as the "Dardanelles landings" as part of the Dardanelles Campaign, where about 480,000 Allied troops took part.
Engagement – tactical combat event of contest for specific area or objective by actions of distinct units. For example, the Battle of Kursk, also known from its German designation as Operation Citadel, included many separate engagements, several of which were combined into the Battle of Prokhorovka. The "Battle of Kursk" in addition to describing the initial German offensive operation (or simply an offensive), also included two Soviet counter-offensive operations Operation Kutuzov and Operation Polkovodets Rumyantsev.
Strike – single attack, upon a specified target. This often forms part of a broader engagement. Strikes have an explicit goal, such as, rendering facilities inoperable (e.g. airports), to assassinating enemy leaders, or to limit supply to enemy troops.
Casus belli – Latin expression meaning the justification for acts of war. In theory, present international law allows only three situations as legal cause to go to war: out of self-defense, defense of an ally under a mutual defense pact, or sanctioned by the UN.
Capitulation an agreement in time of war for the surrender to a hostile armed force of a particular body of troops, a town or a territory.
Strategic surrender – surrender to avoid a last, chaotic round of fighting that would have the characteristics of a rout, allowing the victor to obtain his objective without paying the costs of a last battle.
No quarter – when a victor shows no clemency or mercy and refuses to spare the life of the vanquished when they surrender at discretion. Under the laws of war "... it is especially forbidden ... to declare that no quarter will be given".
Pyrrhic victory – victory with such a devastating cost that it carries the implication that another such victory will ultimately lead to defeat.
Philosophy of war – examines war beyond the typical questions of weaponry and strategy, inquiring into such things as the meaning and etiology of war, the relationship between war and human nature, and the ethics of war.
Militarism – belief that war is not inherently bad but can be a beneficial aspect of society.
Realism – its core proposition is a skepticism as to whether moral concepts such as justice can be applied to the conduct of international affairs. Proponents of realism believe that moral concepts should never prescribe, nor circumscribe, a state's behaviour. Instead, a state should place an emphasis on state security and self-interest. One form of realism – descriptive realism – proposes that states cannot act morally, while another form – prescriptive realism – argues that the motivating factor for a state is self-interest. Just wars that violate Just Wars principles effectively constitute a branch of realism.
Revolution and Civil War – Just War Theory states that a just war must have just authority. To the extent that this is interpreted as a legitimate government, this leaves little room for revolutionary war or civil war, in which an illegitimate entity may declare war for reasons that fit the remaining criteria of Just War Theory. This is less of a problem if the "just authority" is widely interpreted as "the will of the people" or similar. Article 3 of the 1949 Geneva Conventions side-steps this issue by stating that if one of the parties to a civil war is a High Contracting Party (in practice, the state recognised by the international community,) both Parties to the conflict are bound "as a minimum, the following [humanitarian] provisions." Article 4 of the Third Geneva Convention also makes clear that the treatment of prisoners of war is binding on both parties even when captured soldiers have an "allegiance to a government or an authority not recognized by the Detaining Power."
Consequentialism – moral theory most frequently summarized in the words "the end justifies the means," which tends to support the just war theory (unless the just war causes less beneficial means to become necessary, which further requires worst actions for self-defense with bad consequences).
Pacifism – belief that war of any kind is morally unacceptable or pragmatically not worth the cost. Pacifists extend humanitarian concern not just to enemy civilians but also to combatants, especially conscripts. For example, Ben Salmon believed all war to be unjust. He was sentenced to death during World War I (later commuted to 25 years hard labor) for desertion and spreading propaganda.
Right of self-defence – maintains (based on rational self-interest) that the use of retaliatory force is justified against repressive nations that break the zero aggression principle. In addition, if a free country is itself subject to foreign aggression, it is morally imperative for that nation to defend itself and its citizens by whatever means necessary. Thus, any means to achieve a swift and complete victory over the enemy is imperative. This view is prominently held by Objectivists.
Charles Phillips and Alan Axelrod: Encyclopedia of Wars. Facts On File, Inc., 2005, ISBN0-8160-2851-6. (With about 1,800 wars, this is probably the most complete overview in English language).
R. Ernest Dupuy, Trevor N. Dupuy: The Harper Encyclopedia of Military History. From 3500 B.C. to the Present. 4th Edition, HarperCollins Publishers, 1993, ISBN978-0062700568. (With about 1,300 wars this is probably the second most complete overview in English language, with the added value to summarize about 4,500 battles).
Vittorio Ferretti: Weltchronik der Kriege und Demozide - Ein Abriss der Ursachen, Abläufe und Folgen von über 5.000 gewalttätig ausgetragenen Konflikten bis zum Jahr 2000. Amazon, 2014, ISBN978-3000403538. (With over 5,000 conflicts, this German book is by far the most complete overview published in any language till now. Its added value is to include democides into its scope).