Complex sentence: By 1300 Ancient Pueblo People from the Four Corners region abandoned their settlements, likely as the result of prolonged drought from AD 1276 to 1299 which likely caused considerable hardship, such as starvation, raids from neighboring starving people, and dramatic reduction in the pueblo population.
Split into simpler sentences: By 1300 Ancient Pueblo People from the Four Corners region abandoned their settlements. The migration was likely as the result of prolonged drought from AD 1276 to 1299 which would have caused considerable hardship, such as starvation, raids from neighboring starving people, and dramatic reduction in the pueblo population.