Complex sentence: The powerful Ōuchi were also destroyed by a vassal, Mōri Motonari, in 1551; by the end of the Warring States Period only a dozen or so warlord families still remained standing.
Split into simpler sentences: The powerful Ōuchi were also destroyed by a vassal, Mōri Motonari, in 1551. By the end of the Warring States Period only a dozen or so warlord families still remained standing.