Does the outbreak of a major international war change political discourse? Drawing on theories of political communication and elite cueing, identity salience, and threat perception, we hypothesize that the outbreak of a war of aggression by a major power increases the use of nationalist rhetoric by heads of government in other, non-belligerent, states.

To test this hypothesis, we analyse over 10,000 tweets by heads of government from 130 countries before and after the Russian invasion of Ukraine in February 2022. Using word embeddings, we map politicians' tweets along a nationalist–cosmopolitan spectrum and show a significant shift toward nationalist political discourse on the online platform.

Subgroup analysis reveals that this effect was stronger among leaders of member states of the North Atlantic Treaty Organization (NATO). Yet, leaders from countries that are members of the pro-Russia Collective Security Treaty Organization (CSTO) and those with past experiences of irredentism or territorial armed conflicts — thus resembling the Russia–Ukraine war — did not increase their resort to nationalist rhetoric.

These findings offer new insights into how — in the digital age — conflict in one place can diffuse into politics elsewhere.