The world is an unjust place: The impact of lifetime adversity on belief in conspiracy theories.

Conspiracy mentality - the tendency to view important events as the product of secret plots by powerful groups - is known to arise from collective victimization and discrimination. Yet less is understood about how adversities such as illness, financial loss, or trauma, unrelated to social identity, foster such beliefs. Drawing on social and clinical perspectives, we conducted three preregistered studies (total n = 1284) to test whether lifetime adversity contributes to conspiracy mentality via perceived injustice. Study 1 (n = 275) supported this hypothesis, showing an indirect link between lifetime adversity and conspiracy mentality through injustice perceptions. Study 2 (n = 471) employed a controlled comparison group design, showing that victims of violence (vs. non-victims) reported stronger perceptions of injustice, which were positively associated with conspiracy mentality. Study 3 (n = 538) experimentally manipulated perceptions of justice, demonstrating that perceived injustice (vs. justice) increased conspiracy beliefs. While the effect was not significantly moderated by lifetime adversity, exploratory analyses replicated Study 1's mediation pattern. Additional analyses revealed that adversity predicted institutional distrust via injustice and political conspiracy beliefs. These findings advance interdisciplinary understanding and identify the psychological mechanisms linking adversity to conspiracy beliefs, with relevance for understanding social trust and resilience.