Dean_the_Young wrote...
There are, actually: the legality of wars depending on the laws of the state involved, and the agreements made by that state with others.
That's the whole point: each state writes up their own laws according to what the cultural conscensus is. There is no "supreme law" that bars either state from attacking the other for whatever reason. Don't confuse diplomacy with justice.
There are plenty of wars and policies throughout history waged not for 'practical' reasons such as economic or even direct military/strategic advantage, but ideology. The largest failing of the Realist school of political relations is that governments often don't follow the 'practical' rationals.
Just because a state makes an irrational decision doesn't mean it's not trying to gain some sort of material advantage for itself; a dictator may be quite litterally insane but still want something from some neighbouring state that can only be secured through armed conflict. If charismatic enough (or backed by a solid nucleus of insiders, like a ruling party), he'll use whatever ideological gimmick he can to get the population to follow. Ideology is a tool, and is certainly amoral. It doesn't promote ethical virtue, it just promotes whatever suits the state's needs.
It isn't a guarantee, but it is a far better check. The same applies with even non-endorsed special agents: the rule of law doesn't guarantee that the law will always rule, but societies based on rule of law are better than authoritarian fiat.
And as established previously, laws only exist inside individual states. Treaties are made between states and some sort of arbitration mechanism will be set up to settle disputes but there is no "police" oversight. There is only the threat of coercitive measures (authoritarian fiat) that encourages states to honor their agreements. States act neighbourly because they gain from the peace and status quo. When the status quo is no longer acceptable, the gloves come off quickly enough.
There's a word for people who kill others pro bono out of personal conviction, and that word is 'murderer.'
And when they dispense justice and their decisions have force of law, they are hailed as heroes. Would I endorse such a system on Earth? No. Does it work for the asari? Apparently, yes, even if it is an archaic throwback to medieval days. And while Illium is not part of asari space, it IS an asari-dominated world and I think Justicars would think twice before actually trying to hunt an A-Y on any planet not dominantly populated by asari. They understand how law-enforcement work and would probably arrange for local authorities to "flush out" their target and get it deported back to asari space. Omega is a lawless no-man's land, so Samara's authority there was no more or less legitimate than Aria's.