Do external threats decrease political polarization? Climate change and immigration discussions on Finnish Twitter after the Russian invasion of Ukraine

Increasing political polarization poses a serious challenge to democracy. Research has suggested that the rise of an external threat caused by an adversarial state can reduce polarization and increase social cohesion, but the evidence for this claim is mixed. To better understand this phenomenon, we examine whether the external threat posed by Russia's invasion of Ukraine in February 2022 depolarized the divisive topics of immigration and climate change on social media in Russia's neighbor, Finland. By analyzing retweet networks before and after the invasion, we find that polarization decreased, but only selectively. The depolarizing effect was confined to specific subtopics and limited by motivated reasoning - the tendency to interpret new information in a way that fits pre-existing polarized frames. The results suggest that external threats caused by adversarial states can have depolarizing effects, but they are likely to be limited, at least in the context of polarized social media bubbles.