Does armed conflict reduce trade, even in noncombat areas, through the destruction of intergroup social capital? We analyze Ukrainian trade transactions before and after the 2014 Russia-Ukraine conflict. In a difference-in-differences framework, we find that Ukrainian firms from districts with fewer ethnic Russians experienced a deeper decline in trade with Russia. This decline is economically signifi-cant, persistent, and can be explained by erosion of intergroup trust. Affected Ukrainian firms suffered a decrease in performance and diverted trade to other countries. Our results suggest that, through social effects, conflict can be economically damaging even away from combat areas.

How do localized conflicts disrupt supply chains and prompt firms to reorganize them? How do these forces affect firm-level and aggregate economic activity? Using firm-to-firm Ukrainian railway-shipment data before and during the 2014 Russia–Ukraine conflict, we document that firms with prior supplier and buyer exposure to the conflict areas substantially decreased their output. Simultaneously, firms reorganized their production linkages away from partners directly or indirectly exposed to the conflict shock. We build a general-equilibrium production-network model with endogeneous link formation, and we show that our model’s sufficient statistics accurately explains the observed relative decline in firm output once we account for network reorganization. Calibrating our model to the Ukrainian economy, we find that the localized conflict decreased aggregate output in nonconflict areas by 5.5%. This effect increases to 8.4% if we abstract from endogeneous link formation, suggesting that production-network reorganization partially mitigates the detrimental, far-reaching aggregate economic costs of conflicts.

Do new communication technologies, such as social media, alleviate the collective action problem? This paper provides evidence that penetration of VK, the dominant Russian online social network, led to more protest activity during a wave of protests in Russia in 2011. As a source of exogenous variation in network penetration, we use the information on the city of origin of the students who studied with the founder of VK, controlling for the city of origin of the students who studied at the same university several years earlier or later. We find that a 10% increase in VK penetration increased the probability of a protest by 4.6% and the number of protesters by 19%. Additional results suggest that social media induced protest activity by reducing the costs of coordination rather than by spreading information critical of the government. We observe that VK penetration increased pro‐governmental support, with no evidence of increased polarization. We also find that cities with higher fractionalization of network users between VK and Facebook experienced fewer protests, and the effect of VK on protests exhibits threshold behavior.

We provide quasi-experimental estimates of the impact of social media on mental health by leveraging a unique natural experiment: the staggered introduction of Facebook across US colleges. Our analysis couples data on student mental health around the years of Facebook’s expansion with a generalized difference-in-differences empirical strategy. We find that the rollout of Facebook at a college had a negative impact on student mental health. It also increased the likelihood with which students reported experiencing impairments to academic performance due to poor mental health. Additional evidence on mechanisms suggests the results are due to Facebook fostering unfavorable social comparisons.