From The Daily Galaxy:
Imagine a planet dominated by cities like Mega-City One, a megalopolis of over 400 million people across the east coast of the United States, featured in the Judge Dredd comic or "San Angeles," formed from the joining of Los Angeles, Santa Barbara, San Diego, and the surrounding metropolitan regions following a massive earthquake featured in the 1993 movie "Demolition Man."
Don't hold your breath: the 21st century will soon have 19 cities with populations of 20 million or more.
The history of the human species is a history of migration. In 1000 A.D. Cordova, Spain was the largest city. By 1500, Bejing began its rise to power, and 300 years later it was the first city to be over a million people. By 1900 London emerged the world's supercity with over 6 million people. In 1950 New York was proclaimed the first "megacity" with a population of over 10 million people in the greater metropolitan area.
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