  Terrorist attacks not only harm citizens but also shift their attention,
which has long-lasting impacts on public opinion and government policies. Yet
measuring the changes in public attention beyond media coverage has been
methodologically challenging. Here we approach this problem by starting from
Wikipedia's r\'epertoire of 5.8 million articles and a sample of 15 recent
terrorist attacks. We deploy a complex exclusion procedure to identify topics
and themes that consistently received a significant increase in attention due
to these incidents. Examining their contents reveals a clear picture: terrorist
attacks foster establishing a sharp boundary between "Us" (the target society)
and "Them" (the terrorist as the enemy). In the midst of this, one seeks to
construct identities of both sides. This triggers curiosity to learn more about
"Them" and soul-search for a clearer understanding of "Us". This systematic
analysis of public reactions to disruptive events could help mitigate their
societal consequences.
