Even 150 years later, no one can say for sure what started the bloody feud between the Hatfields of West Virginia and the McCoys of Kentucky.

Some think it was shifting allegiances during the Civil War that drove a wedge between the two neighboring families. Others point to a pull-and-tug over land, timber and money. And some feel it was a prized pig, lost or waylaid, that sent the mountain clans into decades of murders and vengeance.

Bits of all those theories, plus a disastrous Romeo-and-Juliet love story, lay the foundation for Historychannel's "Hatfields & McCoys," a six-hour miniseries launching Monday.

"We wanted to show how a series of incidents swept everybody up in this tornado of ego, jealousy, bitterness and violence," said Leslie Greif, one of the project's executive producers, who's been working to get the story to screen for nearly 20 years. "Never forgiving, never forgetting took over, and pretty soon they were in the middle of a war and didn't even know how they got there."

The three-night event stars western-movie veteranKevin Costner, who Greif called "the Gary Cooperof our day." Costner plays Devil Anse Hatfield, a war deserter, entrepreneur and, at times, cold-blooded killer. Also top billed are Bill Paxton as Randall McCoy, patriarch of the McCoy clan, an unrecognizable Tom Berenger as the sociopathic "Uncle Jim" Vance, Powers Booth, Mare Winningham and Jena Malone. The show chronicles about 30 years, a dozen brutal killings and innumerable heartaches in the lives of the two populous families.

Despite its iconic status, there have been few dramatic depictions of the inter-family battle either on TV or in film. It's been portrayed most often as comic or cartoonish — or both, in the case ofWarner Bros.' famous Bugs Bunny musical short, "Hillbilly Hare" — making it ripe for serious treatment, said Nancy Dubuc, president and general manager of History and an executive producer on the miniseries.

"It's a big pre-sold headline that everybody knows but nobody knows," Dubuc said. "It's part of American pop culture, but very few people could tell you the true story of these families."

Costner, whose involvement as a star and producer lighted a fire under the project, said he was attracted to the complexity of the story. As an American-history buff, he had "a working knowledge" of the Hatfields and McCoys and said he welcomed the chance to dig deeper.

"I tried to be an emotional detective," Costner said. "While I thought about the political and economic forces at play — plus the potent combination of alcohol, guns and misery — I wanted to find the humanity in these tough, hardened people."