Complex sentence: The ship was activated by someone, and it travelled to surrounding worlds to pick up its crew, since so much time had passed, there were none of the original troopers left, instead the ship picked up the inhabitants of the planets.
Split into simpler sentences: The ship was activated by someone, and it travelled to surrounding worlds to pick up its crew. Since so much time had passed, there were none of the original troops left, and instead the ship picked up the inhabitants of the planets.