Game of Thrones meets The Predator:
The world Westeros and Essos are located on is a massive game preserve chosen by the Predator species because of its extremes of climate (contrary to common assumption, they are just as home in the cold as they are in the heat, simply preferring extremes of weather to test themselves). They began secretly abducting and transplanting human beings, who retained no memory of the abduction or journey (see:
Predators, the film), from Ice Age Earth and continued bringing subjects up until the medieval era, where they halted technological and social development from behind-the-scenes because that's the era they preferred to hunt, hence the parallels to our Earth's history and subsequent stagnation.
They also transplanted certain now extinct species of Terran animals such as mammoths, aurochs, and dire wolves along with extant species like lions, horses, ravens, goats, etc. In turn they introduced various alien species which they had previously brought to Earth that inspired human myth such as dragons (a skull of which was seen on the Predators trophy case in
Predator 2), giants, and kraken.
The Predators secretly aided their human game at times by giving them "magic" (read: advanced science indistinguishable from magic) to build The Wall because they had introduced nanites capable of resurrecting and animating the dead, who were originally being manipulated and awoken by their telekinetic servants, the alien species called the Children of the Forest, until these White Walkers grew too powerful and out of their master's control. Remnants of this nanite magic also gave rise to wizards and witches and the like who could resurrect the dead, summon spectral assassins, shapeshift, set fire to swords, resist burning, etc.
The Valyrians of old were servants of the Predators, and some of the few humans allowed to know about their masters. They built great pyramids like their ancestors, the worshipers of the Predators on Earth (see:
AvP), some of which can still be found in the city of Meereen. At some point the Valyrian Maesters had outgrown their worship and had begun to harvest the glowing green Predator blood, producing the explosive Wildfire (which amplifies the Predator's self-destruct systems). They had also experimented with advanced Predator alloys to produce Valyrian steel, biological weapons such as Greyscale, and selective breeding of dragons. They eventually revolted against their Predator masters and nearly took one of their ships intact, but at the last moment the last surviving Predator set off the ship's self-destruct, causing the Doom of Valyria that destroyed the ancient civilization completely.
Avatar meets Starship Troopers (Novel):
The Na'vi from
Avatar and the Skinnies from the
Starship Troopers novel (ignoring their appearance in the animated show) are the same species. The description of the Skinnies from the novel could match the Na'vi pretty well:
These geezers are humanoid, eight or nine feet tall, much skinnier than we are and with a higher body temperature; they don't wear any clothes and they stand out in a set of snoopers like a neon sign. They look still funnier in daylight with your bare eyes but I would rather fight them than the arachnids — those Bugs make me queezy. (Ch 1)
...
Nor did we know that strenuous efforts were being made to subvert the alliance against us and bring the Skinnies over to our side; the nearest we came to being told about that was when we got instructions, before the raid in which Flores was killed, to go easy on the Skinnies, destroy as much property as possible but to kill inhabitants only when unavoidable.
https://scifi.stackexchange.com/questions/32160/what-do-we-know-about-the-skinnies
After defeating the human corporate colonists on Pandora, the Na'vi and their few human allies took possession of the human technology left behind in order to defend themselves from subsequent attacks.
The defeated humans meanwhile returned home to Earth, where a new FTL drive system had since been invented that would allow humans to traverse the entire galaxy in search of resources, so defeating the Na'vi took a backseat for a while as they didn't have to rely on only visiting the closest system anymore. During this plundering of the galaxy, the fascist humans encountered the Arachnid species and were again plunged into war. The Arachnids, seeking a base of operations to strike at Earth, colonized the Na'vi / Skinny homeworld. At first, the Na'vi welcomed an ally against further human invasion, but eventually realized the Arachnids were just as willing to exploit them, so they started making peace overtures toward the humans.