Complex sentence: One day Kazan accidentally kills his only ally against the intruders, a large river otter, after mistaking her for one of the beavers; and eventually the entire area around the couple's territory is flooded, forcing them to leave.
Split into simpler sentences: One day Kazan accidentally kills his only ally against the intruders, a large river otter, after mistaking her for one of the beavers. Eventually the entire area around the couple's territory is flooded and they are forced to leave.