Complex sentence: This was due to land purchases from the Native Americans, diseases that the Native Americans contracted from Europeans, and due to starvation from the Little Ice Age, during which Native American corn crops failed and rivers froze, preventing fishing.
Split into simpler sentences: This was due to land purchases from the Native Americans, diseases that the Native Americans contracted from Europeans, and due to starvation from the Little Ice Age. During the Little Ice age, Native American corn crops failed and rivers froze, preventing fishing.