In my home campaign setting I've spent some time working on three sample backgrounds for each major race, divided along social and sub-race lines.
In this I have two major goals: First provide some ideas to players creating characters and second to further flesh out the individual cultures that populate my world.
Gnomes are general divided into three groups: Architects, peasants, and exiles.
Architects are part of the former ruling class of the highly organized and rigidly caste-based gnomish society. Before being conquered by the Iron Empire, these gnomes belonged to the gnome leaders who were directly involved with the cult of Mechanics.
Peasant gnomes where the hoi polloi of gnomish society and have barely noticed the change in management. Though many of the laws that had made them second class citizens have been repealed, most stick to the old restrictions, still not daring to violate what have become cultural norms for the uneducated laborer class.
Exiles are those gnomes that regardless of which caste they had previously belonged too, fled their homeland en masse rather than be ruled by a foreign power.