The aliens, referred to as "The Others," use a calculated series of strikes to decimate the human population:

The 2016 film (known in Portuguese as A 5ª Vaga ) is a science fiction thriller that explores a world devastated by a multi-phase alien invasion. The story follows 16-year-old Cassie Sullivan, played by Chloë Grace Moretz , who must survive increasingly lethal "waves" of attacks while desperately searching for her younger brother, Sam. The Five Waves of Invasion

An engineered bird flu plague that kills a vast majority of survivors.

The total annihilation of the remaining humans by turning their own children into soldiers trained to kill those they believe are aliens. Behind the Scenes Facts Filming: Day One | The 5th Wave Behind The Scenes