so the engineer motive is clear: survival, not invasion.
besides, the aliens are an infestation, not part of the ecosystem; as a matter of fact, alien left to their own device will expand and kill the planet biomass. aliens are there to consume, no less than the engineer.
Same as all other life really.
There is only equilibrium because everything is jostling as hard as it can to outcompete everything else.
Peace is a human invention, it does not exist in nature.
Common core is literally destroying people minds
Ever heard of symbiosis? Countless species not only tolerate each other, they cooperate one another. And yes that includes predators like crocodile and plovers or sharks and remoras.
Ppl here brandishing "totally incorrect" and spouting nonsense.
It's not like if all the foxes suddenly disappeared the rabbits would just reach optimal comfortable population and then start using birth control.
So, equilibrium