Y is their a increase in gangs in my area?

I live in Sacramento and I use to walk everyday from school but when I left this summer 4 mexico when I came back their was northern every were not youngesta older ones like 18 and up just every were in the stop lights around elementry schools almost every park has at least a couple of them their and walkin around I ain't profileing them I know how a northern looks like hair slet back sides cut witch gros in to a mongo and they talk black ***** this ***** that were red somtimes Cortez but red they would blast music like woodie darkroom big tone just want to know how does a all black hood go from all norte in 2 months all I saw was bloods the way I walk and the area I lived was surenos and some bloods and crips and I don't get along with northerns and know that their is one in every spot I just was confused like how the *** does a black hood change in 2 months