> Those wars didn't "cost" trillions of dollars.

Yes, they did.

> The war itself achieves the states political goals, the spending props up the economy.

It props up the economy less then alternative spending of the same ampunt with a higher domestic velocity.

> It pays for itself

It may be a net benefit considering the value of the war aims against the opportunity cost, but that doesn’t change that it has a cost, it just means that (in the right value system) the cost is justified.

No they didn't. Governments don't spend, they invest. That may seem like splitting hairs but it's not. It's not like there were trillions of dollars sitting around waiting to be spent. The real tragedy of war is not that trillions were spent, but that millions of people and resources are poured into it instead of something that improves society.

Your argument of efficiency is inherently flawed. It implies that war is good as long as it's cost effective, which isn't true.

> Governments don't spend,

Yes, they do.

> they invest.

Even if all government spending was investment, investment is just spending in the expectation of future return.

> It's not like there were trillions of dollars sitting around waiting to be spent.

It is literally exactly like that.

> The real tragedy of war is not that trillions were spent

True, that's not the real tragedy of war.

But that's because spending money isn’t tragedy (though the opportunity cost of the choice of how to spend it can be), not because government spending is not-spending, so the trillions spent on war are not-spent.

> Your argument of efficiency is inherently flawed. It implies that war is good as long as it's cost effective, which isn't true.

I thought the context was clear that I was referring to utilitarian justification, whether it is good is a differebt story, sure.

You should educate yourself on macro economics

That’s not how that works. Governments can’t just pay money for things and consider it free so long as they’re employing their own people. Those people could have been employed more productively doing anything else and the entire system is poorer by the amount that the government has spent (to a first approximation).

That is literally how it works. Opportunity cost is only a thing if the private market is willing to capture the excess productive capacity, which it usually isn't. And even then, government has access to levels of scale where they can always be the most efficient employer. Think about the value of building infrastructure vs anything else.