books.google.ca - It was the age of exploration, the age of empire and conquest, and human beings were extending their reach--and their numbers--as never before. In the process, they were intervening in the world's natural environment in equally unprecedented and dramatic ways. A sweeping work of environmental history,...http://books.google.ca/books/about/The_Unending_Frontier.html?id=HQ5KbXYhEB8C&q=slaves&utm_source=gb-gplus-shareThe Unending Frontier
