The idea of “us” versus “them” and the strife that can arise from these arbitrary distinctions is one of the central themes of the novel. It is primarily explored through the relationship between the people of Sparks and the people of Ember, but it is mirrored in several other places. The division begins with Sparks’ inherent distrust of outsiders, and the tangible and intangible differences between the two groups are then used as justification for mistrust and maltreatment. The fact that neither of the groups attempts to reconcile their differences leads to strife, and their responses to strife entrench the arbitrary borders between “us” and “them” even further.

The initial mistrust of the Emberites by the people of Sparks is perhaps justified; the post-Disaster world is a dangerous one. The people of Ember genuinely don’t understand the lack of food and resources that the people of Sparks have had to contend with over the years. The people of Sparks have a genuine need to protect their own from outsiders and from the natural world itself. However, this initial reservation is deepened and justified by the differences between the two towns, eventually leading to violence.

The most obvious differences between the people of Ember and the people of Sparks are physical.