Complex sentence: General Robert L. Eichelberger's Eighth Army was then tasked with conducting a series of amphibious landings in the southern Philippines on islands between Mindanao and Luzon, including Cebu, which was garrisoned by a force of between 14,500 and 15,000 Japanese troops.
Split into simpler sentences: General Robert L. Eichelberger's Eighth Army was then tasked with conducting a series of amphibious landings in the southern Philippines on islands between Mindanao and Luzon, including Cebu. The island was garrisoned by a force of between 14,500 and 15,000 Japanese troops.