The purpose of air power is to contribute to the military's success in peacetime and wartime. Both times it's in the end all about the will of a foreign power: To deter aggression or to force it into accepting our idea of a post-war peace.
The principal ability of air power to deliver such contributions hasn't been questioned for generations, at least not in the case of large and wealthy countries. The best strategy and the limits of air power's contributions on the other hand are subject to renewed discussion during most major violent conflicts with Western participation.
The evidence for limits and quality especially of different strategic air war strategies appears to be contradictory. Didn't win air power the 1999 Kosovo War and didn't it fail utterly over North Vietnam despite much greater loss of lives and property? Air power's ability to win wars without substantial naval or ground manoeuvres appears to be inconsistent - but that's a superficial observation.
This text attempts to resolve the apparent contradictions by paying much attention to the nature of the opposing forces' leadership. It does also attempt to support decision-makers in identifying the most promising approach on a case-to-case basis. Furthermore, it's about truly strategic air warfare; its core is how to persuade the opposing government, not how to crash a war economy (although this fits into the sixth following group).
About the importance of the enemy's character
“If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.”
The first thing to understand when you want to break someone's will is the enemy himself. The opposing leadership has a distinct nature. Different natures may require different strategies for success. This explains in part why strategic air war sometimes failed and sometimes succeeded in pursuit of its strategic goals.
It means as well that anecdotal evidence cannot prove the effectiveness of a certain strategy in general: History lacks examples of ceteris paribus examples and the differences between targeted governments were likely very influential.
It seems plausible to me to define six most relevant groups of opposing governments, based on 20th century military history:
A dominantly rational government is extremely rare, but it's an interesting case. This kind of opposing government is not inclined to wage wars of aggression and is thus rarely if ever an enemy.
A rational being doesn't fall for the sunk costs fallacy and thus doesn't mourn past or inevitable losses. Instead, a rational decision-maker considers only effects that can still to be influenced by its own actions.
The threat of destruction is more potent than actual destruction in this case. Destruction can serve to make the threat more credible, but it also reduces the potential for future destruction. The more you destroy, the less destruction you can threaten with.
The threat of destruction should get primacy over actual destruction as a mechanism for breaking the will of a dominantly rational opponent. It might even be promising to offer reparations for war damages as an incentive. This appears to be practical only in a limited war, of course.
A dominantly irrational government falls for the sunk costs fallacy, and this can work both ways.
It depends on the interpretation of the fallacy whether it provokes more resistance or breaks the same.
The "We have already lost so much, let's not dishonour our fallen comrades!" interpretation improves resilience. The "We already lost so much! Let's end this insanity!" interpretation breaks will. Common to both is the irrational influence of unavoidable outcomes (past losses) on the decision-making. The choice of interpretation depends likely on the character of the person and on how much the person has become emotionally involved.
A campaign that inflicts much damage can fail to break the enemy's will if the irrational government goes with the second interpretation. Such a campaign should thus be reduced to the extent to which it's justified by its support value to decisive land or naval warfare.
A government which is dominated by its greed for power fears its possible loss of power, and this is an effective lever for its adversary. Attacks could be directed at the government's ability to retain its power; at its internal security apparatus, its political organization, its propaganda and at its support from powerful special interest groups. A campaign should hurt the powerful, regime-supporting special interest groups, embarrass the target government and expose its lies.
Popular and institutional support for the government may erode and the government may eventually become convinced that it needs to accept our peace offer's conditions in order to reduce the risk of a political collapse.
A government which is dominated by its intent to serve its country is actually interested in what it perceives as its country's well-being. This may at times simply be national glory. The critical lever against such a government is thus identified easily: Hurt (or threaten to hurt) whatever represents the country's well-being for the targeted government. This happens to be close to the dominant Second World War idea of strategic air warfare, in which much damage has to be inflicted on the opposing country. Tragically, the German and Japanese governments of the time were not pursuing the real interests of their respective people.
A dominantly fearful government is unlikely to be aggressive. A strategic air war against such a government is therefore likely unethical and illegal. There's an impressive historical example for the successful use of air power against such a government: Hitler threatened the Czechoslovakian president Hácha into surrender in March 1939 without any actual fighting. He threatened to bomb Prague and Hácha collapsed. This happened about two years after the devastating and much-publicized bombing of Guernica. Hácha's morale collapse was probably the greatest strategic air power success ever, for it was achieved with very little cost for the victorious aggressor.
A great and credible threat can break the will of a fearful government under certain conditions.
A dominantly resolute government cannot be (easily) threatened or bombed into submission. Germany and the United Kingdom provided such examples during the Second World War.
There's usually the option of foregoing the direct attack on the opposing leadership's will and to employ air power instead in support of land power. Air power can attack land power and its infrastructure directly and it can attack economic targets in order to reduce the sustainment and strengthening of the opposing land power. Air power can also be directed at tactical support of land or naval warfare, foregoing any strategic air warfare.
Alternatively, it may be possible to circumvent the government's resolution by provoking a change of government. It would then be highly advisable to avoid a general bombing campaign that could provoke popular defiance. Instead, the government should be discredited and embarrassed with well-aimed attacks of different kinds. The objective would be to expose the government's inabilities, lies, corruption and other traits that could help their political opposition to replace the government. Such a campaign could be executed with an intentionally very low level of violence in order to avoid an increase of solidarity among the people and their government. Psychological operations and embarrassing actions such as air power displays over the capital in daylight might be more important than bombs in such a strategy.
Actual governments may come close to fit into three of these groups, as the groups basically represent three different opposite pairs. It needs to be investigated on a case-by-case basis which trait is the dominant and thus the one that influences strategic air warfare effects the most.
(It should be added that reality is not immediately relevant when the target is the opponent's will. His perception of reality counts instead.)
These were general strategy ideas for air war strategies against six generic government groups. These strategies are not only about warfare, but inherently political. A good air war strategy is much more than mere selection of targets and dates for high explosives delivery.