In the 500–700 years preceding European contact, the Mississippian culture built large, complex cities and maintained far-flung regional trading networks. Its largest city was Cahokia, which had numerous mounds for different purposes, a highly stratified society, and was located in present-day southwestern Illinois near the Mississippi River. The Native polities of the Mississippian culture fell apart and reformed as new groups, such as the Catawba, due to a series of destabilizing events known as the "Mississippian shatter zone". As described by anthropologist Robbie Ethridge, the Mississippian shatter zone was an area of great instability, in what is now the American South, caused by the instability of Mississippian chiefdoms, high mortality from new Eurasian diseases, construction of a global capitalistic economy based on trading of Native American slaves, and the emergence of Native "militaristic slaving societies".