Just because war is bad does not mean we are forced to throw up our hands and stop making distinctions between degrees of badness. War is not simply infinitely bad... that's ultimately a very sophomoric view.
In industrialized countries, wars of aggression are usually never profitable, but the same can unfortunately not be said for less-developed societies. Even Europe didn't find this obvious until after World War 2. So I guess it ends up being a question of how you define "sophomoric".
"Wealth through superior firepower" has hardly ever been achieved. Even Rome mostly got rich through trade after its armies conquered Europe and North Africa, and a lawful peace was imposed. Had everyone been economically rational pretty much the same end could have been achieved through trade (spoiler: not everyone is economically rational.)
Simple looting of the kind the Spanish engaged in in the New World was never a very good path to wealth, partly because its first effect was to create massive inflation (if you use gold as money and inject vase amounts of gold into your economy without increased productive capacity, you get inflation, not wealth.)
So the conditions of gaining wealth by war are very, very narrowly defined. It's not impossible, but it's amazingly difficult.
There are defensible moral reasons for engaging in mass organized violence--I support the current American efforts to kill people in Northern Iraq, for example--but economic rationality (profitability) is never one of them, because the first step to creating wealth is never to engage in the wholesale destruction of everything the creation of wealth depends on.
Since you brought up Rome in discussing payback for warfare, you could also ask "Cui bono" here -- "who benefits?"
A war is potentially just like a gold rush, the people getting rich are the ones selling the tools to dig or make war.
Just look at my native Sweden, we managed to stay out of a few wars and shamelessly sold high quality steel to the countries fighting. It made Sweden go from the bottom to the top in Europe.
What this implies about lobbying and how wars starts I'll leave to the imagination.
(I might also add that IS has declared war on the democratic world. So trying to stop their expansion is arguably self defence.)
The outcome may be the same, but there's a whole lot more humanity in subjecting someone to the latter.
2. inflicting as little pain as possible: a humane killing.
I pulled it from http://thefreedictionary.com/humane which cites 'Collins English Dictionary – Complete and Unabridged'.
Suffering and harm are distinct things, and being humane is about the former.
When a democracy has a war with a dictatorship it is similar to when the police defends civilians from violence.
(So this don't get into a shouting match: Check "democratic peace theory". I am aware of that the police can misuse their position. A democracy often also do cynical realpolitik when it isn't its voters that gets harmed.)
Edit: You might want to do the distinction of a junta that do a general draft, so there are soldiers for the dictator which didn't volunteer. It isn't an easy solution, but citizens in a country can theoretically overthrow their dictator. Hopefully with more help than the Syrians got from Obama.
Edit 2: I assume that you don't think it is immoral to sell weapons to police. If you are that pacifist, then I think you should move to some place without police to protect you... I hear they have good weather in inner Somalia and southern Yemen. Both are traditional clan societies without police.
Edit 3: Ah, you have a 60s style of police racial violence discussion in the USA right now. I get the down votes.