Well, there were multiple factors contributing to the feud between the Hatfields and McCoys. Firstly, the economic differences and competition for resources like land and timber were significant. Additionally, there were some family honor issues. For example, family members on both sides felt offended by the actions of the other family. Also, the differences in their loyalties during the Civil War added fuel to the fire. The Hatfields were mostly Confederate supporters, while the McCoys were more on the Union side, which led to post - war resentments.