http://www.helium.com/knowledge/45878-overview-social-change-and-urban-growth-in-the-united-states.xml Helium.com > North American Culture > Overview: Social change and urban growth in the United States en-us Copyright Helium.com Wed, 30 Sep 2009 01:00:13 GMT Wed, 30 Sep 2009 01:00:13 GMT