Complex sentence: After 100 years, all surviving Yalaini were pushed back to the island of Dereth, and almost 80 years later, one single Olthoi Queen arrived on the island and began to breed.
Split into simpler sentences: After 100 years, all surviving Yalaini were pushed back to the island of Dereth. After almost 80 years on Dereth, one single Olthoi Queen arrived on the island and began to breed.