Which the "gangs" were mostly irish, italian, and mexican with the only reason blacks weren't included was their limited rights to ownership among other things and their inability to leave their groups of similar race.
And what got the gangs broken up? The elimination of the lower-upper class gap (which is growing again), the introduction of the middle class, the elimination of poor pay/working conditions in factories, and the introduction of ****TONS of new industry to America.
Now, how long do you think that would take to introduce to a group of only a few races whose overall membership only accounts for 1/300th or so of the entire US population (probably much less, that's a gross estimation by my count), and who can't even FIND a job in the inner city. That's why drugs and gang mentality are so rampant--when your family lets you down, and you have nothing, you wanna have everything. Drugs give you money, gangs give you family.
You honestly have no scope of the situation, and are comparing two very different, very...well uncomparable microcosms.