Complex sentence: Suō was ruled for much of the Muromachi Period by the Ōuchi clan, who built a castle at Yamaguchi, but in the Sengoku Period it was conquered by the Mori clan, and was ruled remotely by them for much of the Edo Period.
Split into simpler sentences: Suō was ruled for much of the Muromachi Period by the Ōuchi clan, who built a castle at Yamaguchi. In the Sengoku Period it was conquered by the Mori clan, and was ruled remotely by them for much of the Edo Period.