Empirical evidence of differentiation of “we-ness” and “other-ness” can be found at the level of the immunity system of the human body and at the ethological level in social animals and human beings. Categorization cues to elicit ingroup vs. outgroup discrimination in the animal kingdom are always sensory-dependent and simple in contrast to the cues used by human beings, which are characterized by multiplicity, complexity, and changeability. Because of human beings’ long term and working memory, and social representation and subjective cognition construction abilities, differentiation of ingroup and outgroup members for humans is mainly cognitive and highly dependent on the social context. Categorization cues may retrieve one of many ingroup-outgroup representations built into a person’s long term memory through direct or indirect experience with historical intergroup events. In the past four hundred years of Taiwan’s history, the important ingroup/outgroup categorization cues have been: (1) Pro- vs. against the Ching dynasty; (2) Dutch sovereign government vs. Chinese Han people; (3) Same vs. different immigration origins from China; (4) Same origin but different village residence in Taiwan; (5) Same residence in Taiwan, but with preferences for different folk operas; (6) Japan sovereign government vs. Chinese Han people; (7) Immigration time to Taiwan; and (8) Taiwanese ideology vs. Chinese ideology. While the basic process of categorization cues-ingroup-outgroup differentiation, ingroup favoritism, and outgroup discrimination-has been well established in de-context studies, social identity theory can be enriched by involving social relevant issues and localized historical contexts.