Complex sentence: The two "lions" in front of a shrine are in effect warden dogs called, so called because they were thought to have been brought to Japan from China via Korea, their name is derived from, the Japanese term for the Korean kingdom of Koguryo.
Split into simpler sentences: The two "lions" in front of a shrine are in effect warden dogs called. They were so called because they were thought to have been brought to Japan from China via Korea, and their name derives from, the Japanese term for the Korean kingdom of Koguryo.