This post contains MASSIVE, UNMARKED, UNCIPHERED spoilers for The Banner Saga. And not just plot spoilers either, these are huge emotional and thematic spoilers.
The dredge are introduced in the first game as typical orc stand-ins: an invading horde of implacable monsters with glowing eyes and stone armor, humans stolen and twisted by an unnamed god into his army to depose of the other deities, sweeping down from the furthest frozen north to sack and pillage everything in their wake, lead by a handful of immortal warchiefs (The Sundr definitely give me vibes of the Ten Who Were Taken from The Black Company books). No one is able to communicate with them, they are feared and hated by all, so on and so forth.
So far so orcish.
Move along to game two. Near the midway point you come across a godstone site that the dredge have already visited, and find there the corpse of a dredge woman and a still-living infant. The characters, already suspicious that the encroaching darkness is not all it seems to be, piece together that the dredge are not an invading army - they're refugees, fleeing from the darkness with increasing desperation, putting every able body on the front lines whether or not they are a fighter by trade because there are no other options.
Exactly like you have been doing for a game and a half.
Game three. You get the closest to the dredge that you'll get in the series, with a handful of dredge party members and a human translator (a witch who has learned how to replicate and understand the vibrations they use to communicate.)
Here we get the big bombshell. After the end of the war that killed the gods, the dredge made a secret treaty with the Velka (the council of the most powerful mages) - in exchange for an end to hostilities, they would be taught magic and other crafts they could use to build their own civilization outside of the influence of their god - the survivors had grown resentful of their nameless deity making them for war alone and giving them none of the knowledge and gifts the other peoples possessed.
The second and third generations of dredge are less inclined to war then their forbears, but then the inner sun goes dark and old wounds are re-opened (atop all else, the dredge believe that the Velka have darkened the inner sun and broken their treaty) and the games run their course.
I'll always love LotR's "elves-minus-maslow's-hierarchy" orcs (I'll eat my hat if the thematic parallels between the dredge and Tolkien's orcs weren't intentional.), but the dredge go the extra step of showing what happens when the influence of the Great Evil is no longer at play. You aren't fighting them because they're evil, you're fighting them because there's not enough food.
And that's just it, at the end of the day. An orc is just a man who, broken through the engines of desperation, oppression, ignorance or greed, has been driven to commit terrible violence against his neighbor.
For further reading on the matter, I recommend Emmy Allen's fantastic post and followup tweet. Also Skerples' post. And Arnold's.