Complex sentence: Imperial Japanese Navy and Imperial Japanese Army troops occupied the island since June 6,1942 and had met little resistance, the following action proved to be the deadliest encounter between the opposing forces in the Kiska area.
Split into simpler sentences: Imperial Japanese Navy and Imperial Japanese Army troops had occupied the island since June 6,1942 and had met little resistance. The following action proved to be the deadliest encounter between the opposing forces in the Kiska area.