alternatehistory.com

We define megacity as agglomeration with more than 10 million inhabitants.

Currently, there are four such agglomerations in Europe: London, Paris, Moscow and Istanbul.

What POD would be needed to create another ones by now? I am not sure how far in past we'd need to go back, that's why I'm putting it into pre-1900 thread.

Note: OTL Rhine-Ruhr areas doesn't count since it is polycentric areas too spread out to resemble a single city.
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