Complex sentence: However, Yamashita's order ignored by approximately 10,000 Japanese marines under Rear Admiral Iwabuchi Sanji who chose to remain in Manila, and approximately 4000 Japanese army personnel that were unable to leave the city due to the advance of the American forces.
Split into simpler sentences: However, Yamashita's order ignored by approximately 10,000 Japanese marines under Rear Admiral Iwabuchi Sanji who chose to remain in Manila. Approximately 4000 Japanese army personnel were unable to leave the city due to the advance of the American forces.