blood feud
From Longman Dictionary of Contemporary Englishblood feudˈblood feud noun [countable] ARGUEa quarrel between people or families that lasts for many years, in which each side murders or injures members of the other sideExamples from the Corpusblood feud• There is little middle ground in the ancient blood feud between trial lawyers and the insurance industry.• Rangers' supporters replied in kind, and so the blood feud went on and on - and continues to this day.