Sitting at the southwestern tip of Lake Michigan, one of the largest freshwater bodies in the world, and on the eastern edge of the tallgrass prairies that fill much of the North American interior, early residents in the land that Chicago now occupies enjoyed natural advantages, economic opportunities, and global connections over centuries, from the Native Americans who first inhabited the region to the urban dwellers who built a metropolis in the nineteenth and twentieth centuries. As one millennium ended and a new one began, these same features sparked a distinctive Midwestern environmentalism aimed at preserving local ecosystems.