By 1750, nearly all Native Americans had left New Jersey. 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. Snow storms sent game into semi-hibernation or made them difficult to find. Nut crops such as oak, hickory, beech, walnut, chestnut and butternut failed some years due to late frosts in spring. Many of the Morris County Native Americans went to eastern Canada and others went to the Ohio Valley. The Walking Purchase in September 1737, prevented Native Americans from going to eastern Pennsylvania. At that time, European settlement grew swiftly as there was now land to be farmed and settled.