Livro de Ficção Científica: duas facções alienígenas lutando, eventualmente os humanos se envolvem [duplicado]

Minha sugestão é The Damned Trilogy por Alan Dean Foster .

Você tem duas facções em conflito:

Two major alien civilizations, the Amplitur (a squid-like species with telepathic and mind-controlling abilities - which they couch as "suggestions") and The Weave (a confederacy of more or less equal species), have been fighting a war for several millennia. The Amplitur are attempting to join all sentient species in what they call the "Purpose", an alliance which they "guide" to some unknown (even to them) end. The Weave is a group of species allied in opposition to the Purpose.

A facção que acaba por empregar a Humanidade não gosta de guerra:

...most sentient species in the galaxy have evolved to be incapable of committing violence against other sentients (violence of any sort being most un-civilized, but against another sentient being a [literally] unthinkable crime)...

Eles acham que os humanos são muito bons em toda aquela coisa de luta:

On a mission to find new resources and allies, a Weave scout ship discovers Earth circa late 20th/early 21st century AD and finds that humans are uniquely suited as allies, in that they have the ability to fight. They are adaptable to a wide variety of environments, have few (or sometimes no) compunctions regarding war (humans having been fighting each other for all of their recorded history), and above all seem even more enthusiastic when their aggression is focused on non-humans. Eventually Weave xenopsychologists determine that Earth's fragmented continents resulted in a species that evolved to fight, compete, and kill for dominance. They surmise that all humans are born hunters and killers, but that intelligence is starting to drive them toward the abhorrence of violence that other "civilized" species consider normal.

Pelo menos um personagem está preocupado que a Humanidade possa ser um problema mais tarde:

During the course of her research she comes to the conclusion that unless Humans can be 'civilized' somehow they will eventually turn on the rest of the Weave races once the war is over.

E foi publicado no início dos anos 90! Então, esperamos que seja isso que você está procurando! Em qualquer caso, boa sorte!

Uma possibilidade é a série Death or Glory de Vladimir Vasilyev. Do artigo da Wikipédia:

The novel is the first of four describing the future of humankind among the stars. Humans have acquired faster-than-light travel centuries ago (it's only recently at the galactic scale), but does not progress further. All energetic and ambitious people have moved to new colonies, leaving the Earth to stagnate.

The galaxy is ruled for long by an alliance of five powerful races, mired in an ancient war with extra-galactic Imperishable. Without this war, the Alliance would enslave the Humankind like it treats other newcomers, but now Svaighs just don't have the will and resources. Despite this, most people live in filth and poverty. But the situation changes, when people gain a bleak chance to succeed — and show the Galaxy they aren't going to refuse of it, these Homo with a motto Death or Glory.

Isso se encaixa em que existem basicamente duas facções diferentes, e os humanos não eram inicialmente parte da guerra. No entanto, suas proezas parecem ser em grande parte porque eles são perfeitamente dimensionados para usar a tecnologia Departed Ones, que é superior à tecnologia existente da Alliance. Parece que a principal fonte de conflito é, na verdade, a luta interna pelo poder humano, pois a nave seleciona líderes baseados na personalidade da primeira pessoa para descobri-la, o que não combina com o governo humano.

Existem mais três livros na série, Black Relay , Legado dos Gigantes e No One but Us , cujos detalhes você pode encontrar no artigo da Wikipedia.