Final answer:
The famous feud between the Hatfields and the McCoys started with a quarrel over pig ownership.
Step-by-step explanation:
The famous feud between the Hatfields and the McCoys was sparked by various factors, but a key flashpoint was a quarrel over pig ownership. The families had differing socio-economic backgrounds, political affiliations, and even fought on opposite sides during the Civil War. This led to a long-term violent feud, where anything from a verbal dispute to a conflict over property could set off a cycle of violence and retaliation.