Go read Jared Diamond's (author of Guns, Germs, and Steel) report in Harper's Magazine, The last Americans: environmental collapse and the end of civilization. Then donate a few dollars to the Red Cross or other aid agencies working in South Asia (tangentially connected, but it must be said). From the report:
One of the disturbing facts of history is that so many civilizations collapse. Few people, however, least of all our politicians, realize that a primary cause of the collapse of those societies has been the destruction of the environmental resources on which they depended. Fewer still appreciate that many of those civilizations share a sharp curve of decline. Indeed, a society's demise may begin only a decade or two after it reaches its peak population, wealth, and power.