Okey, this is a more measured response. I apologize for my over-reaction.
From the outsiders perspective, any and all subject vaguely referring to america quickly become preaching by one or both of the One True Faiths of American politics.
It is incredibly irritating. My point was not 'This particular American war', it was 'looting wars in general'
Back on track, the Rachni (admittedly probably Indoctrinated), are having a good go at making a war of conquest work.
At least in this universe the question of 'Is interstellar war even possible', is a resounding yes.
Well, again, it really depends on the economical and political context.
Given that, unlike Rachni, we will likely bother with caring for conquered population
and, unlike Rachni we do not want to piss off several tier-1 powers, it's going to be problematic. Plus Rachni, IIRC, were 'sponsored' somewhat by Reapers, so there is that advantage too.
Better example would be Krogans tbh. Krogans had a decent go at it since they were breeding extremely fast and, too, did not care about opinions of other factions.
Point is, Rachni and Krogans are somewhat unique in that they had unique predisposition for the type of war of aggressive conquest: poor diplomacy, cultural lack of empathy, extremely fast breeding allowing them to exploit resources and replenish losses fast.
We, on the other hand, are not breeding all
that fast (I've touched upon it already when I talked about how I am sceptical about us keeping the trend of exponential growth - IMO we are going to run into limits of what our population can do soonish), are going to be reliant on diplomacy (Asari and Volus parts due to old connections; plus, well, trade). And we don't really have a cultural disregard for the exploited natives to the degree Rachni, Krogans or British had, as far as I can think, although it is too early to tell.
If we try to rely on war too much, we are less likely to be next British Empire and more likely to be next North Korea. We can try and pull a Krogan: be big bad war heroes and use political capital to get some serious concessions. Krogans kinda got way out of line there in the end, but in theory, contributing enough to war to make sanctioning us in response for some of more mild acts of assholery is possible. But that's never going to be as blatant as Rachni or Krogans.
As an aside about Krogans.
IMO Bioware fucked up when they basically transplanted Orks into ME without regard for "in space, guns should be more important than tough biology".
With Rachni it made more sense; I have no idea how on earth Krogans manages the "logistics" part of interstellar warfare against Citadel space; Rachni had an excuse in "hivemind", "time to prepare" and "Reapers did it". The only thing going for Krogans is post-Rachni-War decline in militaries and Krogans getting some time to expand before anybody thought (or had political capital) to reign them in.
Like, when they were at war against Rachni, they had Citadel handling the industry part; but Krogans were not that great at industry or whatever, so how come they were succeeding enough to warrant genophage? IMO, it's kind of silly grimderp-inducing move by the Bioware more than anything.