When did New York City, Chicago, and L.A. become Alpha cities? (housing)

[ColdAilment]

Throughout their history, New York City, Chicago, and Los Angeles have all received rapid growth, putting them at the top of the list for being the largest metropolitan areas in the United States today, and making them all world class cities. This was not always so, 150 years ago Los Angeles was a small town of less than 10,000 people.

My question is, when did these cities, and other major American cities carrying the Alpha title, take this mantle? When did they truly become a world class city and how?

[ELR123]

NYC: Second half of the 19th century, in the context of WORLD cities. It's been a major US city since the beginning.

Chicago: Right around the turn of the century, simply due to industrial power. Didn't really develop further than that until later.

Los Angeles: I would say the 50's I suppose. Some would argue '40s.

[Spikett]

Los Angeles really took off during WWII because of the war industries (planes, etc). Lots of good jobs and thousands moved here. The San Fernando Valley housing boom really hit in the 50s and, as they say, the rest is history. The freeway system was also started in the 40s.

[MB8abovetherim]

Let's not forget they have very productive ports. NY and LA are no-brainers but Chicago was at one time as well. In the 19th and early 20th centuries half of the US merchant marine sailed on the Great Lakes. Chicago with it's Lakes port and it already being THE railroad hub in the US made it a big player.