Complex sentence: As time passed, the airline's Saipan traffic decreased due to the breakup of the Trust Territory of the Pacific Islands, which was subdivided into smaller political units, fewer people needed to travel to the capital of the trust territory.
Split into simpler sentences: As time passed, the airline's Saipan traffic decreased due to the breakup of the Trust Territory of the Pacific Islands, which was subdivided into smaller political units. Because of the breakup, fewer people needed to travel to the capital of the trust territory.