Why is Chicago caled the second city?

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Why is Chicago caled the second city?

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Chicago used to be the second largest city in the United States. However, Los Angeles took over the '2nd' spot several years ago...but 'second city' still sticks since Chicago held that title for so many years. Chicago is now the third largest city in the U.S., followed by Houston, Tx.
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is it the second biggest city in the usa
because its not as big as new york
It comes from Chicago historical position as the nation's second largest city, although it has actuallly slipped to third behind L.A.
http://www.chipublib.org/004chicago/chin...
According to Wiki - this is a reference to the rebuiling of the city after the great fire. It also has been referenced due to Chicago being second to NY. We also have a famous comedy club that is called The Second City where many of the comedians get their training at.
http://en.wikipedia.org/wiki/list_of_nic...