Stop all preparations! We must attack the Dragon Rider's nest at once! We will take down their Alpha! Then we will take Berk!
~ Drago commanding his army.
The Northern Alliance is the main antagonistic faction of the How to Train Your Dragon animated franchise. They appear in DreamWorks' 29th full-length animated feature film How to Train Your Dragon 2, and DreamWorks' 36th full-length animated feature film How to Train Your Dragon: The Hidden World. It was founded and led by Drago Bludvist, who is bent on creating an army of dragons to take over Berk and the rest of the world to himself and his forces. The army is later bequeathed to the Warlords.
When he was a little boy and lost his family to dragons, Drago vowed to rise above dragons. So he sets himself to conquer the world by using the dragons. During his conquests, he then found a Bewilderbeast hatchling and raised it with cruelty until it become subservient to him. He then formed the Northern Alliance composed of Dragon Trappers from numerous nations such as Slavic, Sami, Inuit, and Asiatic, along with thousands of enslaved dragons. He also built many traps, weapons, and armor made for his enslaved dragons.
How to Train Your Dragon 2
During much of the plot, The Northern Alliance are seen aiding their master in capturing more dragons before turning their attention in helping take down the dragon's Alpha, which happens to be another Bewilderbeast raised and cared by Valka, the mother of Hiccup Haddock (the protagonist of the series). Though Hiccup and his friends, along with his father Stoick, manage to help fight off the Northern Alliance and free some captured dragons, it was all in vain when Drago's Bewilderbeast defeats and kills Valka's Bewilderbeast, allowing it to take control of the dragons (including Toothless) and kill Stoick, much to the delight of Drago and his soldiers.
How to Train Your Dragon: The Hidden World
After Drago was killed after his attempt to destroy Berk was foiled by Hiccup, which forced his Bewilderbeast to retreat to the Hidden World, The Northern Alliance were taken over by his other followers, the Warlords. The Warlords hire Grimmel the Grisly to bring them Toothless so they can use the latter to control the other dragons and conquer the world.
Later on, after Grimmel leads the Warlords and their army to New Berk's location and succeeds in capturing Toothless and the Light Fury, he goes to the Warlords, who wait so they can capture Toothless. However, Grimmel betrays them, revealing that he was planning to kill Toothless all along. The Berkian Dragon Riders then arrive on the scene and prove to be no match to the Northern Alliance once more. By the end of the ambush, while Hiccup and Toothless go to rescue the Light Fury and take down Grimmel, the Northern Alliance members, and possibly even the Warlords, are either killed or injured. Anyway, no matter if there were any survivors or not, Drago's former men were ultimately rendered useless and purposeless, as Toothless and the other dragons retreat into the Hidden World, where they would remain until humankind can coexist peacefully with them.
Drago Bludvist (founder and former leader).
Krogan (former second-in-command).
Warlords (Ragnar the Rock, Griselda the Grievous and Chagathai Khan, former seconds in commands and current leaders).
Drago's army in How to Train Your Dragon: The Hidden World.