Complex sentence: The Japanese launched their attack on Port Moresby over the Kokoda Trail from Salamaua, a seaport on the north coast of New Guinea, and when the attack failed, turned the port into a major supply base.
Split into simpler sentences: The Japanese launched their attack on Port Moresby over the Kokoda Trail from Salamaua, a seaport on the north coast of New Guinea. When the attack failed, the Japanese empire turned the port into a major supply base.