The abundance of information on social media has reshaped public discussions, shifting attention to the mechanisms that drive online discourse. This study analyzes large-scale Twitter (now X) data from three global debates -- Climate Change, COVID-19, and the Russo-Ukrainian War -- to investigate the structural dynamics of engagement. Our findings reveal that discussions are not primarily shaped by specific categories of actors, such as media or activists, but by shared ideological alignment. Users consistently form polarized communities, where their ideological stance in one debate predicts their positions in others. This polarization transcends individual topics, reflecting a broader pattern of ideological divides. Furthermore, the influence of individual actors within these communities appears secondary to the reinforcing effects of selective exposure and shared narratives. Overall, our results underscore that ideological alignment, rather than actor prominence, plays a central role in structuring online discourse and shaping the spread of information in polarized environments.

翻译：社交媒体上的信息泛滥重塑了公共讨论，使人们的关注点转向驱动在线话语的机制。本研究分析了来自三个全球性辩论——气候变化、COVID-19和俄乌战争——的大规模Twitter（现称X）数据，以探究参与度的结构动态。我们的研究结果表明，讨论并非主要由特定类别的参与者（如媒体或活动人士）塑造，而是由共享的意识形态一致性所驱动。用户持续形成极化社区，其中他们在某一辩论中的意识形态立场可预测其在其他辩论中的立场。这种极化超越了具体议题，反映了更广泛的意识形态分裂模式。此外，在这些社区内，个体参与者的影响力似乎次于选择性接触和共享叙事所产生的强化效应。总体而言，我们的研究结果强调，在结构化在线话语和塑造极化环境中信息传播方面，意识形态一致性而非参与者知名度起着核心作用。