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Well, since the map is based on the novel, the main goal for players is to destroy (for the side of good) or capture (for evil) the ring. And it doesn't matter who does it.
As for the plot, it's more complicated. I wanted to convey it, of course, but the actions of the players and computer opponents can be different, not as in the book. And all of this will look a bit strange. If it were possible to set a specific victory condition for each player, that would be a different story.
P.S. By the way, I downloaded all the maps and campaigns from these links. One or two of them are worth paying attention to, as maps based on Lord of the Rings. The others don't even have the names of the main characters. And at the same time, they are all geographically incorrect, more like the map author's own vision of Middle-earth.