Complex sentence: To disarm Baekje, he sent a Buddhist monk named Dorim, who went to Gaero's court with the secret objective of corrupting the country before the invasion of Goguryeo.
Split into simpler sentences: To disarm Baekje, he sent a Buddhist monk named Dorim. Dorim went to King Gaero's court, with the secret objective of corrupting the country before the invasion of Goguryeo.