Public opinion scholars have long worked to identify the factors leading citizens to form coherent political attitudes, yet comparatively little attention has been given to the possibility that national political environments systematically affect belief system constraint. By modeling political beliefs as dedicated statistical networks based on social surveys covering 38 European countries between 2002 and 2020, I show that national-level belief systems vary substantially and systematically in attitude constraint. I theoretically motivate and empirically support a path mediation model that explains country-level belief system coherence as jointly driven by the elite- supply and mass-demand for programmatic party-citizen linkages. Compared with elite-centered explanations, bottom-up drivers such as dense civil society organizations and high levels of civic activism emerge as surprisingly strong and direct predictors of mass belief coherence. Furthermore, where symbolic, ideological identities are central to people’s political attitude systems, mass beliefs tend to be more coherent overall.