The Gears of War franchise follows the Fenix family starting with Marcus Fenix as he attempts to survive ten years after E-Day. The Emergence Day was when the Locust threat was unleashed upon the planet of Sera killing millions.
After those ten years, Marcus' best friend Dom breaks him out of prison and they head out to deal with this threat. The second game follows the group and focuses on Dom searching for his wife and protecting the last human stronghold of Jacinto. The third and final game in the original trilogy is the end of the world where Lambent are rising and the last of Delta Squad works to stop the new threat and Locust.
Gears of War 4 was a bold new step in the franchise following JD Fenix and his friends many years later in a completely different Sera that's being ravaged by storms. The Swarm is a new threat and it's up to the next generation of Gears to deal with it.
In the fifth main entry Kait takes the focus, as she finds out about her past and deals with a growing Swarm threat. There's lot of danger, action and change as the game heads into an open world environmnent of play.