That's really interesting. To put it another way, economic opportunity costs apply to armed conflict.
You can even extend this beyond purely defensive wars.
The most obvious extension is pre-emptive wars. A great example would be the Six Days war (aka the 1967 Arab-Israeli war). Israel knew that they were about to be attacked (the massed units on their borders were not subtle), and instead attacked preemptively. Arguably, this reduced the cost of the war for them in a number of ways. First, by seizing the initiative and the element of surprise, they likely reduced their combat losses relative to what they would have experienced if they had waited for their neighbors to attack. Even more importantly, the entire war was fought outside of their then-borders, so their infrastructure was not damaged by the fighting.
Clausewitz even makes a case for starting a war that you know you are going to lose. That sounds crazy at first, but in some scenarios it makes sense, because it's not just about the balance of power, it's about the direction in which that balance is shifting. If you are highly certain that another country is going to attack you, and that you will lose, you have to consider whether your defeat would be more or less severe in six months or a year. If the balance of power is shifting in your favor, you want to postpone hostilities as long as possible. If, on the other hand, the balance of power is shifting in favor of your enemy, you want to precipitate a war as soon as possible in the hopes of securing a better position to sue for peace. Either way you know you're going to lose, it's a question of how badly you are going to lose.
Finally, even a war of naked aggression could have a nearly immediate net positive impact on your economy if your forces are so superior that you will suffer minimal losses, and if you capture valuable resources as a result, or if you secure tactically valuable terrain that reduces your losses in an impending conflict. The German annexation of the Sudetenland is a prime example of this.
You can even extend this beyond purely defensive wars.
The most obvious extension is pre-emptive wars. A great example would be the Six Days war (aka the 1967 Arab-Israeli war). Israel knew that they were about to be attacked (the massed units on their borders were not subtle), and instead attacked preemptively. Arguably, this reduced the cost of the war for them in a number of ways. First, by seizing the initiative and the element of surprise, they likely reduced their combat losses relative to what they would have experienced if they had waited for their neighbors to attack. Even more importantly, the entire war was fought outside of their then-borders, so their infrastructure was not damaged by the fighting.
Clausewitz even makes a case for starting a war that you know you are going to lose. That sounds crazy at first, but in some scenarios it makes sense, because it's not just about the balance of power, it's about the direction in which that balance is shifting. If you are highly certain that another country is going to attack you, and that you will lose, you have to consider whether your defeat would be more or less severe in six months or a year. If the balance of power is shifting in your favor, you want to postpone hostilities as long as possible. If, on the other hand, the balance of power is shifting in favor of your enemy, you want to precipitate a war as soon as possible in the hopes of securing a better position to sue for peace. Either way you know you're going to lose, it's a question of how badly you are going to lose.
Finally, even a war of naked aggression could have a nearly immediate net positive impact on your economy if your forces are so superior that you will suffer minimal losses, and if you capture valuable resources as a result, or if you secure tactically valuable terrain that reduces your losses in an impending conflict. The German annexation of the Sudetenland is a prime example of this.