The share of adults in the United States who are married or cohabiting fell from 66.8 to 61.7 percent between 1995 and 2025. Over the same period, partisan animosity increased by two-thirds. We estimate how much rising partisan aversion—or reluctance to partner across political party lines—has contributed to the decline in partnership. We measure partner preferences using a discrete choice experiment. Respondents are willing to give up about 70 percent of a potential partner’s annual income to partner with someone from their own party rather than the opposing party. To isolate the effects of partisan aversion from those of other economic and social changes, we estimate an equilibrium matching model. The model incorporates these preferences and segmented meeting opportunities that limit available partners. We fit the model to regional data on couples and singles. The estimated model explains political sorting primarily through partisan aversion and educational sorting primarily through segmented meeting opportunities. Reducing partisan aversion to its mid-1990s level, while holding other determinants of partnership fixed, would raise the share of married and cohabiting adults by 1.6 percentage points, or about 30 percent of the decline since 1995.

We study fertility in a dynamic spatial equilibrium model with endogenous location and residential choices, alongside investments in children’s education. We estimate the model using near-universal administrative microdata from South Korea, drawing on census records, credit bureau data linked to mobile phone mobility records, and government administrative sources. Our estimates indicate that high commuting and housing costs, combined with intensive education investments in large cities, where the amenity of living is large, substantially reduce fertility. We conduct a decomposition exercise to explain the sharp decline in South Korean fertility over the past decade, finding that rising education and childcare costs play a significant role. Finally, we conduct a series of counterfactual exercises considering place-based policies to reduce commuting costs, increase housing supply, or lower education costs. We find that policies focusing exclusively on large cities, such as Seoul, may have the opposite effect on fertility than intended due to spatial sorting. However, a combination of nationwide policies targeting the fertility margin directly can boost fertility significantly.