The share of adults 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. To isolate the effects of partisan aversion from those of other economic and social changes, we develop and estimate an equilibrium matching model. The model incorporates partner preferences elicited in a discrete choice experiment and allows segmented meeting opportunities that limit whom people can meet. We fit the model to regional data on couples and singles. In the estimated model, party sorting is driven primarily by experimentally measured reluctance to cross party lines, while education sorting is driven primarily by segmented meeting opportunities. Reducing partisan aversion to its mid-1990s level, while holding other determinants of partnership fixed, would raise the married-or-cohabiting share by 1.5 percentage points, 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.