The Hatfield Clan
I will wait until I can watch all three episodes at once. As much play as this famous American feud in the Appalachians gets, the roots go back to the English–Scots border between 1200 and 1600. Read the book by George MacDonald Fraser, The Border Reivers. These were warring clans on both sides of the border. Nationality didn’t matter. Hadrians Wall, or what’s left of it was not THAT much of a barrier.
It’s peaceful along that border now. The major fighters were deported, first to Northern Ireland, then in the 18th Century to the Appalachian borders.
The feuds along the Anglo-Scottish border lasted centuries.