Again, while a good argument can be made that the Gambinos rivaled the Genovese for about 35 years (from the late 1950's to early 1990's), there is really little to no evidence that they ever supplanted them.
What happened in the late 1950s that suddenly made the Gambinos rivaling the Genoveses for the number one spot? Just because Carlo took over all of a sudden they became a force to be reckoned with? I think both families as rivals goes back to the days of D 'Aquila and Masseria. So if you have to choose a timeframe I'd say the 1920s to the early 1990s.
"It was between the brothers Kay -- I had nothing to do with it."
