Interindividual cooperation mediated by partisanship complicates Madison’s cure for “mischiefs of faction”

Significance How can a pluralistic republic combat dangers of tyrannical factions? In Federalist No. 10 , James Madison proposed that the problem of factions could be mitigated by expanding the political sphere. Over 200 y later, however, polarization plagues the United States, despite the likely greater diversity of issues considered in the realm of politics. To tackle this puzzle, we explore how, in a partisan context, interactions among regular citizens can lead to collective-level factionalization via diversity collapse, as issues/opinions become increasingly segregated by party. We find that, while Madison was right that issue diversity can promote both individual cooperation and societal cohesion, extreme partisanship can introduce tension between the two, so that interindividual cooperation thrives at the cost of increased polarization.