As early as the 15th century, a few individuals ventured into the Wild Fields, the southern frontier regions of Ukraine separating Poland-Lithuania from the Crimean Khanate. These were short-term expeditions, to acquire the resources of what was a naturally rich and fertile region teeming with cattle, wild animals, and fish. This lifestyle, based on subsistence agriculture, hunting, and either returning home in the winter or settling permanently, came to be known as the Cossack way of life. The Crimean–Nogai raids into East Slavic lands caused considerable devastation and depopulation in this area. The Tatar raids also played an important role in the development of the Cossacks.