Abstract. Despite their similar political agendas, sub-state nationalist movements in the industrialised West align themselves on different positions along the left–right spectrum. Through an analysis of Belgian sub-state nationalist movements, this article proposes an explanation for this phenomenon by focusing on critical junctures. In particular, the focus is on the difference between Walloon and Flemish nationalist labour movements. Walloon nationalism has historically been led by socialist trade unions, while Catholic trade unions form a core part of the Flemish nationalist movement. The article seeks to explain this pattern by analysing the critical political alliances formed during the introduction of universal suffrage. The elections of 1894 established socialists as the dominant force in Wallonia and Catholics as dominant in Flanders. The emerging pillarised social structure ensured the reinforcement of the initial choices.