Complex sentence: In the meantime, the Japanese secretly decided to abandon Guadalcanal and withdrew to the west coast of the island from where most of the surviving Japanese troops were successfully evacuated during the first week of February 1943.
Split into simpler sentences: In the meantime, the Japanese secretly decided to abandon Guadalcanal and withdrew to the west coast of the island. From that location most of the surviving Japanese troops were successfully evacuated during the first week of February 1943.