Straight from conspiracy theories on the internet, Tribes explores the premise of an alien invasion of Earth.

Earth's top-secret Space Force is decimated when the Myrmidons, a race of ant-like creatures commonly known as the Brood, invade the Sol System. The Black Fleet and the Earth Defense Force Fleet, two breakaway societies whose sole mission is to protect the solar system, flee and head to the Galactic Federation’s capital world. They address the federation council and bring help to fight the invaders. When the Myrmidons invade Earth and take out the power grid, the fabric of society breaks down. People band together for protection and flee the cities. They hide in the mountains and deserts, forming into various tribes for protection.

John Carpenter, a US Army veteran, is taken aboard a Brood ship and held as a slave. On Crylon-5, John is sold and forced on board a Myrmidon warship. He is trained to become a Mamluk, a warrior slave. In the process, John leads a slave rebellion and takes the ship with the help of his fellow slaves. The former slaves join forces with the Black Fleet and the Earth Defense Force Fleet and head back to Earth to rid the planet of the Brood. Will they be victorious and help user Earth into a new age of peace and prosperity, or will the Brood slaughter the population, taking humans as slaves and laying the planet to waste?