Most scholars currently agree that war is, in part, taking place online. Yet, few studies have provided systematic insights into this new dimension of war, where everyone with an internet connection—whether within or outside the warzone—is now a potential online warrior. How does war in this "new dimension" pan out? And to what extent is this online war fought in response to, or in isolation from, the physical battlefield? In this paper, I study how online contentious dynamics respond to conflict on the ground by estimating the effect of conflict intensity on the likelihood of engaging in uncivil communication on Reddit. I draw on three full archives of posts from war-related, English-language, member-heavy subreddits (r/IsraelPalestine, r/syriancivilwar, and r/UkrainianConflict) to study contentious dynamics online. Comments and posts are classified according to their support for conflict parties and their degree of (in)civility, using supervised machine learning. Using conflict event data from a variety of sources that track daily casualties, the location of strikes, and the affiliation of their victims, I estimate the relationship between conflict intensity and online incivility in war-related subreddits. The findings contribute to our understanding of the transnational democratic potential of digital war discussions through their (lack of) alignment with the ideals of deliberative democracy while highlighting a potential transnational cause of political polarization.