Warfare and ritual

Introduction
Wesley Clark decided to speak out about the current US engineered government swaps since 9/11 (Wesley Clark on 9/11 policy coup). It's part of a tradition of professional soldiers speaking plainly about the dissatisfaction with what they are used for. "War is a racket" by Smedley Butler is an older reproach, highlighting that he "might have given Al Capone a few tips".
"Weapon systems and political stability" is a dated and unfinished manuscript by the economist Carroll Quigley. It contains lots of nuggets of ideas and insights. The aforementioned soldiers act with an idealism that is at odds with reality.
This idealism comes from a system of concepts that legitimize extreme inter human violence by putting it into ritual frameworks. Different societies and political movements do not share exactly the same ritual frameworks, but usually achieve some common rituals in order to have limited conflicts. An inability to find a common ritual leads to an open bottom spiral of violence that in theory can only be solved by completely killing one side.

The American way of occupation
The American way of war has been to shower occupied lands with money as a herbicide against insurgents rising against benefactors and "swimming among the population like fish in water" (Mao). Sometimes shower heads are missing or the supply gets too diluted and manipulated for the desired effect. This makes the USA a force of good as they convincingly try to help other people, unlike previous empires who took without spending. The lands conquered in recent times, since 9/11, all contain vast riches of natural resources and US companies do often, but not exclusively, directly profit from the exploitation of these resources. Their profits stand in no relation to the expenditure by the American state and thus taxpayers. Even as a giant Ponzi scheme for private enrichment exploiting a lobby-able state, it makes a very poor show in comparison to straightforward embezzlement practised by different elites.

Sea and land power
It starts to make more sense if you take a classic sea power point of view. A sea power controls the sea lines of communication that in human history have always been used to transfer the greatest quantity of goods over the greatest distance with other methods being insignificant in weight per distance statistics of overall transports. A land power by contrast controls the places where certain goods are produced and usually depends on sea powers to allow transport and trade. A sea power is capable of influencing the water transport network and only through participation in a network of mutual exchange can people with differing advantages maximise the profits from their output. A sea power traditionally provided a large tonnage of transport vessels, but is not required to because in the essence it's about controlling the flow of goods, not providing it. From a sea powers point of view, the quest for power is about control of available opportunities for themselves and against their enemies. For this task they can from time to time muster their assets to divert the stream of goods as required. The US is extending influence on the flow goods landwards in some places with the intent of improving their ability to manipulate the global flow of goods. Benefits don't derive from occupied lands, but from the economic paybacks of network control paid in totally different places another time. A land power can transfer over land  many humans to violently convince or kill others. Over sea the transport of goods has always been optimal, but in slotting through humans it provides a bottleneck. Going over sea required to achieve a mutual agreement, while moving continental could be less enticed for an understanding. As outlined above, the rituals of warfare serve as enabler of understandings to limit violence. You can consider the current US as an example of a sea power mentality that needs mutual rituals for their conflicts.

Denial of rituals and enforced ritual
I outlined the effect of denial of ritual on violence above. Genocides are an example of such a case of not achieving a mutual ritual, not due to a lack of understanding, but pretended deafness and cunning.
The Japanese attack against Pearl Harbour is an often cited example of a clash of different ritual concepts. The US operated according to the Western system that consider such an act most dishonorable as the ritual dance of weapons needs an official introduction for all participants to get ready in their costumes. The Japanese had their own tradition that considers declarations of warfare as a great folly because it gives an enemy time to get dressed for the show and perform with less embarrassment. Japan tried during this war to further exploit a denial of common ground rituals such as surrender and was faced with weapons of indiscriminate mass-murder like firestorms and nuclear bombs, until they agreed to a show of Western rituals to finish the Japanese instrument of surrender. No guerrilla insurrection followed, even Unit 731 handed over their gruesome data and Japan was recreated as a state according to US views.
The Taliban of Afghanistan by contrast have not yet signed any such instrument or participated in a similar show. In Iraq this went well with the Baath party's grip on power fading away and being replaced by different alignments. In the tribal society of Afghanistan the US opposition is entrenched in the majority, not the minority tribe, of Pashtus and it does not appear like things will follow a similar route.
Despite this lack of mutual recognition, there's neither an indiscriminate mass-slaughter of these people. A solution to ritual denial is partial ritual recognition by a group that has insider knowledge on the population base of opponents. This is often called a puppet regime because they do have to comply to a foreign power. It's important for their credentials and effectiveness to show a tolerable level of resistance. Like most people in power, they can use that force to settle private scores and gain benefits with hubris leading to scorn and separation from the population with corresponding loss of insider knowledge and effectiveness at population control. The mindset makes the difference. Humans can readjust their worldview and memory if given a convincing chance to do so and every society has a mechanism for transporting guilt on someone in order to stabilize the order of the rest. The game is about creating scapegoats and in a civil war it's hard not to be guilty if you're allied with the creators of this mischief by their invasion.
Germany and Japan had the advantage of falling into their own cultural guilt trap from which they could be rescued by the foreign invasions. Instead of civil war, social ostracism was exercised within these societies on some scapegoats, who could not convincingly claim to have been innocent or coerced. These were the ones who had brought the perils of war and occupation upon the others.

Why?
The why of the rituals seems clear, it limits violence by reaching some common ground of understanding and acting together instead of mutilating and killing each other.
Why is there warfare? As per above it results from an extreme unwillingness to cooperate with each other. Non-cooperation is understandable as a denial of perceived unfair exploitation, but also as a claim to status, benefits and as attempted coercion.
After the latest episodes of very bloody warfare all over the world, the former major powers have changed their ministries of military affairs into defence ministries in order to secure moral grounds. This moral ground has extended the necessary amount of rituals for a legitimate declaration of warfare. There was yet no major master of ceremonies, who totally failed at creating these necessities, unlike many minor players at war. The moral ground is often only a stimulus package derived from the right performance of pre-war rituals for getting into war frenzy.
The Chinese are not wrong that this is a rigged international system and are reluctant to participate. Voilà, you have a human conflict that includes billions of people.Would they create something that is not rigged?

There are many reasons for fighting or not fighting a war. Real reasons can be justified, pretending wrong reasons can serve better. It's all very obvious in everyday conflicts.
Have you ever met someone who never had any conflict?