One of Clausewitz’s most famous statements is that “war is nothing but a continuation of political intercourse, with a mixture of other means.” The concept of warfare describes the rational purpose of a war.

An important point is the meaning of politics. It is not “policy” in the sense of abstract government decisions. Politics is the total sum of human social interaction. It is the way groups make decision relating to each other and their environment. It includes government, culture, economics and other aspects. War is the use of coercion to achieve political goals and it cannot be separated from the political causes and ends.

Politics and economics are decisions that manage scarce resources with alternative uses. Resources are not infinite, so these resources must be allocated for one of many possible purposes. There are distribution problems which must be resolved. Politics aggregates the preferences of the group and authorizes political violence to force all individuals to abide by the group decision. All societies utilize political violence or they would fall into anarchy. Likewise, there are distribution problems between states in the international arena, but international relations exist in anarchy.

This brings us to war, which is just an elevated form of normal political violence. Since resources and values are finite, individuals will have conflicting preferences. So “War… is an act of violence intended to compel our opponent to our will.” This represents the rational decision to maximize your utility by using power to change the decision of your competitor. War is a form of adaptation in politics.

Clausewitz first discusses politics as the rational foundation of the theory of war.

“We see, therefore, that war is not merely a political act, but also a real political instrument, a continuation of political commerce, a carrying out of the same by other means. All beyond this which is strictly peculiar to war relates merely to the peculiar nature of the means which it uses. That the tendencies and views of policy shall not be incompatible with these means, the art of war in general and the commander in each particular case may demand, and this claim is truly not a trifling one. But however powerfully this may react on political views in particular cases, still it must always be regarded as only a modification of them; for the political view is the object, war is the means, and the means must always include the object in our conception.”

War is politics and it solves the distribution problem through coercion. War can never be separated from the underlying political and distribution problems. It is not an independent thing.
Back to Clausewitz:

We maintain, on the contrary: that war is nothing but a continuation of political intercourse, with a mixture of other means. We say, mixed with other means, in order thereby to maintain at the same time that this political intercourse does not cease by the war itself, is not changed into something quite different, but that, in its essence, it continues to exist, whatever may be the form of the means which it uses, and that the chief lines on which the events of the war progress, and to which they are attached, are only the general features of policy which run all through the war until peace takes place. And how can we conceive it to be otherwise? Does the cessation of diplomatic notes stop the political relations between different nations and Governments? Is not war merely another kind of writing and language for political thoughts? It has certainly a grammar of its own, but its logic is not peculiar to itself.

Accordingly, war can never be separated from political intercourse, and if, in the consideration of the matter, this is done in any way, all the threads of the different relations are, to a certain extent, broken, and we have before us a senseless thing without an object.

There is a sarcastic expression that Diplomacy is war by other means. The two are inseparable.

There is a difference between Politics and Policy, which are easily confused. Policy is a final product of politics, and to some extent the final result of a political war is the policy. This tells us nothing useful since we cannot know the end results fo war beforehand.

The government is not a unilateral rational actor and it operates within the Trinity of rational, irrational, and non-rational elements. It does not set policy.

The enemy government is acting rationally to win as well. This is a contest between intelligent enemies who adapt and counter each others will. This is a multi-state conflict where allies and neutrals have different interests and constrain strategies and policies. The international competition is obvious enough.

Domestic politics plays a major role as well. There are special interest groups who vie for power and resources within governments. Any structural theory (such as Realism) which declares the state a unitary rational actor will inaccurately predict its behavior.

The opposition faction acts rationally to impede the rationality and success of the ruling faction. Court intrigue has been one of the most common features in all wars throughout time. Ambitious politicians who are out of power will use any war as an opportunity to undermine and weaken their governing rivals, even if this causes their country to lose the war. They will slander and defame the wartime leaders as incompetent or unfit to rule.

This is rather easy to do, if highly deceptive. They simply assign non-rational effects of the war to the President and Generals, as if the ruling faction intended these unforeseen consequences. They play upon the irrationality of the public and deceive them.

In the past, Roman Emperors were wary of military campaigning. If they sent a talented general to fight a war, that general may win, become popular, and decide to become the next Emperor by force of arms. If the Emperor chose to campaign himself, then politicians back in Rome would plot behind his back. This is a reoccurring feature in all societies, from the Persian and Chinese Empires, to the United States today.

Sometimes dissent is based around constructive criticism (which I categorize as helpful). There is a more crass dissent that wishes to lose a war in order to win political power.

There is much more to Politics in warfare than domestic and international competition. Politics is about managing the Trinity of elements and the non-linearity of its effects. States try to rationally push these forces in a direction beneficial to the state. This accounts for behavior of armed forces in both intrastate and interstate warfare.