Complex sentence: During World War II the islands were first occupied by the Japanese who established a small base in April 1942 near the village of Rossun on Manus Island and built the first landing strip merely by manpower at the eastern Point of Los Negros Island in Momote.
Split into simpler sentences: During World War II the islands were first occupied by the Japanese who established a small base in April 1942 near the village of Rossun on Manus Island. They also built the first landing strip entirely by manpower at the eastern Point of Los Negros Island in Momote.