New York City is sometimes called “Capital of the World” because it’s home to the United Nations. This unofficial title is seldom written as “the world’s capital” or “the world capital.”
   
Wall Street is said to give New York City the title of “World Capital of Capital” or “World Capital of Capitalism.” Both titles have been seldom used. “World Capital of Capitalism” is cited in print from 1967; “World Capital of Capital” is cited in print from at least 1991.
 
 
27 April 1967, Corpus Christi (TX) Times, “Stalin’s Daughter SHows Charm, Openness, Poise” by Saul Peet, pg. 12E, col. 2:
One assumes Svetlana Alliluyeva is aware of her father’s image in America and of the many ironies attending her presence in the world capital of capitalism. Only 20 minutes from Wall Street, she shows no fluster.
   
Google Books
Rainmaker: The Saga of Jeff Beck, Wall Street’s Mad Dog
By Anthony Bianco
New York, NY: Random House
1991
Pg. 13:
... assets through the medium of high finance — through Wall Street, the world capital of capital, which enriched itself in the 1980s as never before.
     
New York (NY) Times
The World Capital of Whatever
By HAROLD FABER;
Published: September 12, 1993
(...)
Many cities and states have dual claims to being world capitals, but New York City outdoes them all. Not only is it truly the world capital as the home of the United Nations but it is also the world capital of capital because of Wall Street. More than that, though, it also bears the title of world capital in the following categories:
 
Advertising, art, the arts, art theft, bagels and lox, communications, corruption, credit card crime, dance, entertainment (disputed by Las Vegas, Nev.), food stamp fraud, glamour, herring (many European cities would certainly question that), jazz (New Orleans would differ), media, noise, pop music, private schools, publishing, skyscrapers (but Chicago has the tallest building in the world), theater (I, however, would opt for London) and youth unemployment.
   
Google Books
Friends in Deed:
Inside the U.S.-Israel Alliance
By Yossi Melman and Dan Raviv
New York, NY: Hyperion
1994
Pg. 37:
“I actually started liking America,” Kollek says as he thinks back to his first encounter with the world capital of capitalism.
   
New York (NY) Times
THE AGE OF DISSONANCE; Urban Lemonade, 75 Cents
By BOB MORRIS
Published: September 22, 2002
(...)
’‘Who are you giving the money to?’’ the man persisted.
 
’‘To me,’’ Ian answered.
 
Hey, it’s hard to blame a child for thinking that way, growing up as he is in the world capital of capitalism.
     
New York (NY) Daily News
NEW YORK, THE VAMPIRE STATE
Sunday, January 2th 2005, 6:56AM
New York State, home to the world capital of capital and business, is suffering a slow drain of economic power that’s best measured by its record in creating jobs. Over the past decade, New York has fallen behind the nation in expanding employment.
 
New York (NY) Times
April 1, 2008
On Paper, Wall Street Gets Its Way
By JENNY ANDERSON
More than a year ago, when the markets were flying high, a chorus of alarm went up on Wall Street. Talk spread that the United States risked losing its edge in the financial world.
(...)
Proponents of the principles approach say it is more efficient. They point to the meteoric rise of London as a global financial center, which has fueled worries that New York might one day lose its title as the world capital of capital. The Financial Services Authority, Britain’s main financial regulator, relies on principles rather than rules.
   
New York (NY) Times
What Red Ink? Wall Street Paid Hefty Bonuses
By BEN WHITE
Published: January 28, 2009
By almost any measure, 2008 was a complete disaster for Wall Street — except, that is, when the bonuses arrived.
 
Despite crippling losses, multibillion-dollar bailouts and the passing of some of the most prominent names in the business, employees at financial companies in New York, the now-diminished world capital of capital, collected an estimated $18.4 billion in bonuses for the year.