Previous parts in Worldbuilding From Reality are indexed here:
We all know what humans will go to war over. Don't we? We are human, after all -- certainly we understand what makes us kill each other?
After all, we've been doing it a good long while. At least 7300 years, it seems.
Will your readers think they understand human warfare?
The usual excuses are fights over resources (water, hunting, grazing, flint deposits, etc) And of course, there's Helen of Troy - men go to war over women, or maybe just to get away from the yammering in the house?
Humans get angry, blame their internal discomfort on others, and HIT.
Kindergarten kids learn to hit before they learn to speak coherently. It's human to HIT that which annoys, discomforts, or obstructs.
Today, the external annoyance, obstruction etc. is coming from people who have banded together under a different political banner.
We are gearing up to fight to the death over IDEAS, and usually over differing ideas of what reality is.
Here is an article on motivated reasoning.
In theory, resolving factual disputes should be relatively easy: Just present evidence of a strong expert consensus. This approach succeeds most of the time, when the issue is, say, the atomic weight of hydrogen.
But things don’t work that way when the scientific consensus presents a picture that threatens someone’s ideological worldview. In practice, it turns out that one’s political, religious or ethnic identity quite effectively predicts one’s willingness to accept expertise on any given politicized issue.
And below that, in the same article:
The same facts will sound different to people depending on what they already believe.
DENIAL DOESN’T STEM FROM IGNORANCE
The interdisciplinary study of this phenomenon has exploded over just the last six or seven years. One thing has become clear: The failure of various groups to acknowledge the truth about, say, climate change, is not explained by a lack of information about the scientific consensus on the subject.
Instead, what strongly predicts denial of expertise on many controversial topics is simply one’s political persuasion.
In other words, humans make up their minds, then keep an open mind about facts.
If you are writing Alien Romance, you can be confident you will portray the human as recognizably human in their thinking processes. But why would that human fall in love with this particular Alien?
What Alien thinking process is so sexy?
Look at some of the research mentioned as arising over the last six or seven years -- find a single, simple, easily explained and illustrated principle that the Aliens do differently. Find why that would be so sexy!
One method of manufacturing Alien species touted by Poul Anderson was simply that all behavior, cultural and philosophical is sexual.
If the reproductive process is different (say egg laying, for example) the Alien cultures would develop from and around the differences caused by that different process.
All human cultures we've ever discovered have that element in common -- so it is very hard to see how reproductive processes generate our cultures and our civilizations.
Warfare, and winner-takes-all-including-the-women, is one thing all our civilizations have in common -- and shrewd analysis can reveal how warfare is essentially sexual.
The whole sex/violence spectrum that is studied so closely by the Romance Genre writers will lead inevitably to the larger type of combat - armies, and massacre.
We, and all your readers, are descendants of the winners.
Remember that -- winning is all-important to us because of it. There are no losers left. So this is now major league, Super Bowl warfare.
This election season is dubbed a war for the soul of America. It might actually be that, a spiritual war.
Would your Aliens understand that? Would their lack of ability to understand being descendants of winners be their most endearing characteristic?
If your Alien hears an impassioned political speech from this election war, will he understand it? Will he know why your human female protagonist is willing to give her life, or at least her love-life, to add even her own tiny bit of force to her side's winning?
Could they understand war between winners?
Or the obverse -- caught up in some Alien, interstellar war for Alien reasons (having to do, unknown to the Aliens, with their Alien sexuality) would your human protagonist have any idea why they were killing each other, blowing up planets, exploding stars - destroying life in the galaxy over their Alien issues?
Viewed from the human's eyes, their facts will sound different than they would to any Alien from any Alien side.
Incorporate this oddity of human nature which makes our ability to deny not a result of ignorance, but rather of what we already know (and thus can't question) into a novel about human/Alien Romance. Contrast the human need to make war with the Alien war - can they comprehend the relationship between sexuality and violence?
Astrology gives you a good clue as you study the 8th House, Scorpio, and its ruler, Pluto. Scorpio is not sweet-love like Libra. And Pluto, being the upper octave of Mars is not about fighting and quarreling, but about war and warfare.
What is the "outer-planet" of the Alien's solar system, what does it rule in their character, and how does your individual example of this Alien people manifest that property?
Build your Aliens from the reproductive level up through sexuality, and on into becoming the dominant species on a planet.
While you are doing that, consider that human dominance on this planet might be coming to an end. After all, all previous dominant species came to their ends.