by Gabe BullardIn 40 years, America will be a younger, more diverse and more populous nation. That's according to author and urban historian Joel Kotkin, who visited the University of Louisville Thursday.Kotkin cites America's high rates of birth and immigration as primary factors in shaping the nation's future. The younger and more diverse population, he says, will give the country an economic edge with nations with older populations.But Kotkin says the next generation will have to overcome the problems caused by the current population."We left an enormous mess: overvalued real estate, overvalued stocks, much too much de-industrialization, a regulatory environment that's very hostile to entrepreneurship," he says.Kotkin also predicts that more Americans will live in small cities and close to their families by 2050.To hear the full interview with Kotkin, click here (MP3)