Background
The Archenlanders are the human people of Archenland, the northern kingdom that borders Narnia. In the Chronicles they tend to represent a healthier form of human kingship and culture than the imperial system of Calormen. Archenland is not portrayed as perfect, but it is honorable, hardy, and closely tied to the northern moral world.
How the Race Functions in Narnia
Archenlanders are important because they stand between Narnia and the ambitions of the south. Their stories often involve loyalty, rightful inheritance, and the defense of a smaller but better-ordered kingdom. Lewis uses them as a contrast to both tyranny and decadence.