Community Interaction and Conflict on the Web

User-defined communities are an essential component of many web platforms, where users express their ideas, opinions, and share information. However, despite their positive benefits, online communities also have the potential to be breeding grounds for conflict and anti-social behavior. Here we used 40 months of Reddit comments and posts (from January 2014 to April 2017) to examine cases of intercommunity conflict ('wars' or'raids'), where members of one Reddit community, called "subreddit", collectively mobilize to participate in or attack another community. We discovered these conflict events by searching for cases where one community posted a hyperlink to another community, focusing on cases where these hyperlinks were associated with negative sentiment (e.g., "come look at all the idiots in community X") and led to increased antisocial activity in the target community. We analyzed a total of 137,113 cross-links between 36,000 communities.