Historically there was sometimes the idea that citizens are the property of the sovereign to use or dispose of as he sees fit. A lot of historical international law had the view that states have absolute feeedom to conduct their internal affairs however they saw fit.

Luckily we have largely moved past that view.

I think as a purely practical matter, moral outrage is shaped by who controls the information space. If you are a country being invaded, you probably have an organized, well funded communication department to tell your side. If you are an Iranian protestor, not only do you not have that, you don't even have internet at all because the state cut off all means of communication.

> something I don't really understand is that one nation killing another is more immoral than when a nation does this to their own domestic population.

I don’t know that anyone thinks a state’s violence against its citizens is less immoral. It’s more that countries are more hesitant to get militarily involved in the domestic affairs of another country because it would mean essentially declaring war against that state. But in a conflict between states, an outsider can more easily support one side militarily without declaring war against the other side.

“A country that violates the rights of its own citizens, will not respect the rights of its neighbors.”

That’s from my readings of philosophy.

But yeah, I do recognize the same sentiment as you found. I think philosophy itself is an answer: most philosophies explicitly champion dictatorships, under whitewashed terms. Ever heard something like “society is a big organ transcending individual needs”? We got it from Hegel.

Because the international order is fundamentally anarchic, while domestic orders are (supposed to be at least) nomic, structured by law and rights. Yes, there are attempts at creating international law, but these amount to treaties more than a structured, visible, governing law.

> I've read a ton of philosophy and something I don't really understand is that one nation killing another is more immoral than when a nation does this to their own domestic population.

Which books say that?

> What makes intra-state politics more acceptable to use violence?

Acceptable? It's more about the consequences or lack thereof, the incentives

History has shown that pretty much nothing happens to the regime unless two coalitions of countries invade from both sides simultaneously, and that's like, not going to happen

>I've read a ton of philosophy and something I don't really understand is that one nation killing another is more immoral than when a nation does this to their own domestic population.

Who holds this opinion?

>But for some reason, humanity doesn't seem to care as much.

All of humanity cares less about when a government uses violence against its citizens than wars?

How can you possibly make this generalization when each internal conflict is different just like every war and how difficult it is to measure sympathy

> one nation killing another is more immoral than when a nation does this to their own domestic population.

I don’t think that’s a particularly established moral position.

that's because they weren't shooting crowds already assembled in the streets and going into hospitals nationwide to find the injured. Nazi Germany was aiming to maintain plausible deniability in the concentration camps for as long as possible, while parallel competing plans for what to do with the population were being explored and failing. (there were other solutions before and alonside the final solution)