Political polarisation on social media in different national contexts

The present dissertation examines the phenomenon of political polarisation on social media. Specifically, the dissertation addresses the question of how the intensity of polarisation and the ideological lines along which it occurs might vary between different national contexts. First, it explores the differences in the intensity of political polarisation on Twitter in 16 democratic countries (Article 1). Second, it examines the ideological lines along which polarisation occurs in two non-Western contexts, specifically among Russian (Article 2) and Ukrainian (Article 3) users of Vkontakte – a social media platform popular among users from post-Soviet states. The dissertation demonstrates that the levels of political polarisation differ dramatically between countries. In democracies, polarisation tends to be lowest in multi-party systems with proportional electoral rules (e.g., Sweden), and the highest in pluralist two-party systems (e.g., United States). It also shows that, in non-democratic non- Western contexts, polarisation does not necessarily run along the left–right spectrum or party system lines. In authoritarian regimes or those with less stable party systems, polarisation runs along the lines of other issues that are more politically relevant in a given context. In Russia, polarisation manifests itself along pro-regime vs anti-regimes lines, whereas in Ukraine, polarisation happens around geopolitical issues. Polarisation on social media thus tends to reflect existing political cleavages and their intensity, in line with the theory of political parallelism. The major implication of this dissertation in the context of research into polarisation on social media is that findings on the topic from single-country studies that come from Western democratic contexts should be interpreted with caution, as they are not necessarily generalisable. To make generalisable inferences about the relationship between social media and political polarisation, more comparative studies are needed, as well as studies that take into account platform affordances and the causal mechanisms that might drive polarisation