Mutual resentment between nations/families/tribes etc.
Excerpted from Jordan Peterson's Book, 12 RULES FOR LIFE.

Mutual resentment piles up when families/nations/groups do not address their bitterness to the other and whistle in the dark instead.
Everything untidy (hate/loneliness/frustration), is swept under the carpet and the dragon feasts on the crumbs day to day.
It is easy to keep the peace for a short while but the dragon feasting on the crumbs is getting bigger.
The dragon feasting on the crumbs under the carpet grows big, pulls the house from its foundation and can't be then ignored. All unexpressed and hidden issues come out in ugly ways like Noah's flood draining everything.
No one built an ark yet they saw the big storm gathering.
Communication would require admission of terrible emotions; resentment/hate/loneliness/betrayal and many other unaddressed emotions.
JORDAN IS A SMART-A$$, Vulnerbale too but thats life. I want 12 more rules ahahhaaha