As polarization increasingly shapes social life in contemporary democracies, hostility toward residents of other
regions or states in a country has emerged as a growing phenomenon, particularly in federal and decentralized
countries. This paper explores the potential of indirect positive reciprocity to mitigate territorial outgroup
prejudice in the aftermath of the catastrophic flood that struck the Valencia region on 29 October 2024.
Occurring amid intense political polarization and glaring multilevel coordination failures, the disaster sparked
a remarkable wave of civic mobilization and horizontal interregional solidarity, most notably the large-scale
deployment of firefighters from other Spanish regions. Their efforts were widely praised by local communities
and garnered substantial media attention. Leveraging this unique context, we conducted a survey experiment
to assess whether cooperative interventions could reduce territorial prejudice. Our findings show that territorial
bias endures – even in the face of extraordinary postcrisis intergroup solidarity – underscoring the deep-rooted
nature of regional like-dislike patterns in polarized political environments.