Complex sentence: When Jadis first entered Narnia at its creation, she fled to the north after eating a fruit that gave her immortality, where she spent nine hundred years gathering strength to invade and conquer Narnia, causing the 100 years Winter.
Split into simpler sentences: When Jadis first entered Narnia at its creation, she ate a fruit that gave her immortality. Then she fled to the north, where she spent nine hundred years gathering strength to invade and conquer Narnia, causing the 100 years Winter.