Complex sentence: In 611 Imseong left Baekje for Japan known at the time as "Yamatai" and the Japanese called him Rinshō Taishi because that was the Japanese reading of his name.
Split into simpler sentences: In 611 Imseong left Baekje for Japan known at the time as "Yamatai". The Japanese called him Rinshō Taishi because of the Japanese reading of the characters in his name.