Continuing fight between parties, families, clans, etc.

One word substitute is Feud.

Enmity: a state or feeling of active opposition or hostility.
Feud: a prolonged and bitter quarrel or dispute.
Quarrel: a heated argument or disagreement, typically about a trivial issue and between people who are usually on good term.
Skirmish: an episode of irregular or unpremeditated fighting, especially between small or outlying parts of armies or fleets.