Like the Astors, the Rockefellers and the MacArthur Foundation, the Kennedys gained much of their wealth by playing the NYC real estate market: As Skyscraper Dreams: The Great Real Estate Dynasties of New York by Tom Shactman observed in 1991:
"Few realized that Joseph Kennedy Sr. had made the bulk of his fortune through owning pieces of Manhattan, or that the Rockefellers' incomes derived as much from Manhattan real estate as from their oil interests...In the space of a single decade, by speculating in New York real estate, Kennedy tripled his fortune. After his spree, he devoted his money...to furthering his sons' careers in politics."
In his 1964 book The Founding Father, Richard Whalen described how JFK's father operated in NYC during the 1940s:
"Kennedy moved into promising situations, exploited them, and quickly moved out...He bought a property at 51st Street and Lexington Avenue for $600,000 and later sold it for $3,970,000; another at 46th Street and Lexington Avenue cost $1,700,000 and sold for $4,975,000; still another at 59th and Lexington cost $1,900,000...and sold for $6,000,000...In September, 1944, the general welfare committee of New York's City Council heard complaints against Kennedy from tenants in the Siegel-Cooper Building, a West Side loft building he had bought the previous year..."