Aristotle said that man is a political animal. Benjamin Barber, on the other hand, says man is an urban animal. With over 78% of the western world living in cities, Barber suggests that since there are scores of international, inter-city, and cross-border city based institutions that are working together to deal with the world’s largest challenges people will look to mayors of these cities, rather than presidents and prime ministers to be the leaders of the 21st century.