deep-seated hatred

Translations
глубоко укоренившаяся ненависть
The conflict was fueled by deep-seated hatred between the two groups.
Конфликт подпитывался глубоко укоренившейся ненавистью между двумя группами.
Definitions
A strong and persistent feeling of animosity or aversion that is firmly established and deeply rooted in a person's emotions or beliefs.