THis is what i believe and what i have or will state in my story, The Oddworld Story:
Glukkons were originally scavengers by nature, there own continent (before they moved in to Mudos) was puny and when they saw mudos and the physical of mudokons they became jealous. As a result, they became a lonely species, reflecting in their jelousy until they built a massive wall around there continent to keep other people from seeing in. THey could still look out however, and when sligs and vykkers united to make pants, they gathered an army of sligs to come and beat up the mudokons and then became industialized as their jelousy was fed and was turned in to greed.
That's just my idea though. It's probably far from the truth.