I'm sympathetic to your view because I used to hold it.
> I think they have to be ethical standards. If they are economic standards then you open up the possibility that any method of war/killing is acceptable in dire economic circumstances.
Why should any method be acceptable? Why not have (for example) Donald Trump and Kim Jong Un put on boxing gloves and determine the fate of NK's nuclear program with a boxing match?
The US has been enacting sanctions on NK for decades which have caused significant suffering of NK's population. The pain and suffering caused by those sanctions, the starving children, etc., are viewed by the US to be the fault of NK's leaders simply because they do not obey US directives.
From the perspective of the US, the sanctions are a humane way of putting pressure on NK's regime that are nonviolent. Are the pangs of hunger felt by the children who are starving or malnourished due to those sanctions nonviolent?
In international conflict, all that matters is one nation's ability to force another nation's hand. Imagine if NK were able to do something to cause Americans to miss three meals per week until the US backed down from its extreme position on NK's regime. We laugh about this because it is so unlikely, but what is the difference?
The hawks will tell us with a straight face that KJU is mentally unstable. Note that all leaders that the US wishes to remove from power are labeled mentally unstable or insane and unpredictable. Our propagandists leverage the fear that many people feel for mental illness and label the enemy with it to make us more easily mistrust and hate the enemy.
By every rational account, KJU is playing a cool, long-term game and is using his power and resources effectively to stave off US bullying. While I would certainly prefer he not have nuclear weapons, there is no evidence that he is unstable or irrational. He simply hasn't gone for the carrots that have been halfheartedly offered, and multiple US presidents have failed to improve the situation.
Is KJU supposed to simply say "OK, Donald Trump, I will step down because I would never threaten to launch a nuclear weapon at a country that declares my regime illegitimate and threatens me with military operations in nearby waters"? It's pretty absurd to think he'd do that. His incentive at this point (based on what has been offered) is to make the US worry that any strikes or attempts to unseat his government could result in a nuke being launched at one of the population centers of the US or a US ally.
Note that KJU has not threatened nuclear war in isolation, it has simply threatened to respond if attacked.
> Those standards evolve over time.
What has occurred is that the US now has much more control over which wars it wishes to enter, and has a more difficult time persuading citizens to risk their lives fighting. So the sort of military that we have today is designed to allow wars to continue in spite of the lack of obvious threats. Since the threats are not obvious, it is not possible to convince the American people to carpet bomb a country that is not obviously at war with us, so a more surgical method must be used in order to get enlistees for optional wars.
The moral progress narrative is just that, a narrative. If we ended up in a fight with a true adversary we would throw it out the window and use all sorts of newly developed weapons (such as EMF weapons that peel the skin off of enemy soldiers, sound weapons that deafen the enemy and cause months of headaches, etc.).
War is about force and coercion, and war requires public support in a democracy. Those two things are (I believe) the fundamentals from which all of the rest of the scenarios (technology, morality, etc.) fall out.