The concept of absolute war was a philosophical construct developed by the military theorist General Carl von Clausewitz. This concept was featured in the first half of the first chapter of his most famous book, On War. In it, Clausewitz explained that absolute war is a philosophical abstraction--a "logical fantasy"--that is impossible in practice because it is not directed or constrained by political motives or concerns, nor limited by the practical constraints of time or space. He called warfare constrained by these moderating real-world influences real war.
In his explanation of absolute war, Clausewitz defined war as "an act of violence intended to compel our opponent to fulfill our will". However, war itself does not contain inherent moral or political aspects. These conditions (for instance, the laws of armed conflict) are placed on war by those who fight it, and exist because the intelligence of the civilized nations involved exercises greater influence on their methods of fighting war than does their instinctive hostility.
Absolute war can be seen to be an act of violence without compromise, in which states fight to war's natural extremes; it is a war without the 'grafted' political and moral moderations. In On War, Clausewitz explains what makes up absolute war:
The three Reciprocal Actions 
An utmost use of force 
Clausewitz states that "...it follows that he who uses force unsparingly, without reference to bloodshed involved, must obtain a superiority if his adversary uses less vigour in [the] application [of force]". Therefore, war in its most natural manner would involve each state continually reciprocating each other's use of force (plus some) to maintain a superiority, until both were using violence to its utmost extent. This is the first reciprocal action, and leads to the first extreme of war.
The aim is to disarm the enemy 
Clausewitz stated that the purpose of war is to make the opponent comply with the will of the nation or state. However, an opponent will obviously not do that unless complying to that will becomes the least oppressive of its available options. Therefore, in order to make the enemy comply with the will of the nation, a state must place its adversary in a position that is more oppressive to it than compliance. Furthermore, that position cannot be temporary, or appear to be temporary. This is because it will be more likely that an enemy will simply 'ride out the storm' in the prospect of being in a better position at a later stage. Any change in this position would be a change for the worse, and so in order to best achieve this position a state must disarm its enemy (forcing it into a position from which it cannot resist).
Furthermore, as war involves two (or more) hostile states, this principle applies to both, and so it becomes the second reciprocal action, whereby both try to impose such a position on the other.
An utmost exertion of powers 
Here Clausewitz states that if a state wishes to defeat its enemy it must annihilate them. According to Clausewitz, the use of power involves two factors. The first is the strength of available means, which may be measured somewhat by numbers (although not entirely). The second factor is the strength of the will which can not be specifically measured (only estimated) as it is intangible.
Once a state has gained an approximation of the enemy's strength of resistance it can review its own means and adjust them upwards accordingly in an effort to gain the advantage. As the enemy will also be doing this, it too becomes reciprocal (the third reciprocal action), creating a third push towards an extreme.
Confusion with Total War 
The recognition of total war since World War I has created a degree of confusion for many, who fail to understand the differences between it and the concept of absolute war, often using the terms interchangeably and blaming Germany's conduct of "total war" on the writings of Prussian military theorist Carl von Clausewitz. In reality, however, Clausewitz neither coined nor used the term "total war," and "absolute (or ideal) war" is quite a different concept.
Total war is essentially a war in which the home front (that is, a state's political system, society and economy) is mobilised to a massive degree for the continuation and expansion of the war effort--it implies the subordination of politics (internal and external) to the goal of purely military victory. It is characterised by civilian infrastructure and civilians themselves becoming highly involved in war as part of the military's logistical support system.
Absolute war on the other hand, is war that reaches its logical extremes (as mentioned above) when it is free from the moderating effects that are imposed on it by politics and society, not to mention the practical constraints of time and space. As wars cannot run themselves, and require politics and society to exist, Clausewitz held absolute war to be impossible, as it could not avoid these influences.
Although most of the confusion over "absolute war" is the result of sloppy reading (or no reading) of Clausewitz's actual discussion in Book One of On War (the only part of Clausewitz's unfinished draft that he considered to be in finished form), some careful readers point out that there are several references in later sections of the book (which, somewhat confusingly, are derived from earlier drafts) to "absolute war" that reflect an earlier conception of such war as simply the more extreme reaches of the forms that Napoleonic warfare had actually achieved. This conception, however, was clearly rejected by the mature Clausewitz.
See also 
- Clausewitz, Carl von, On War, Book One, Chapter 1. The standard translation today (though probably not the most accurate version) is Carl von Clausewitz, On War, ed./trans. Michael Howard and Peter Paret (Princeton: Princeton University Press, 1976, revised 1984). Many unsophisticated writers reference the Penguin Classics version, dated 1968. This severe abridgement, a Vietnam War-era treatment (its hostility is aimed primarily at "neo-Clausewitzian" Henry Kissinger, not Clausewitz) is based on the archaic 1873 translation. The best translation, not currently the standard simply because the copyright-holder has failed to promote it, is Karl von Clausewitz, On War, trans. O.J. Matthijs Jolles (New York: Random House, 1943).