here's one answer:
In the 1970s in Los Angeles gang turf was designated by a geographic radius on purely social terms. When Tookie Williams from the west side formed an alliance with Raymond Washington from the east LA they morphed into the Crips gang. The Crips gang became a monicure for subsets within the gang. These groups would aid each other in street fights. The geographic area deemed Crip territory would be patrolled by Crips gang members and couldn't be breached upon by other gangs. With the advent of crack cocaine in LA in the 1980s, gang territory became and is presently devised based on drug turf. That is, high level dealers control an area by enforcers, who are apart of the gang that the dealer claims, as well as low level dealers - who are able to make money under the protection of their supplier and gang within a geographic location which is lucrative solely to those players. Expansion of a set’s turf is usually a sure way of expanding drug distribution, thus extension of lucrative feedback.
The difference between the past and present is the stronger emphasis on drug dealing presently. The value systems have changed.
Although this is an example of LA gangs, it can be applied to many other gangs in different regions. Today, gang turf is primarily related to drugs.
I recommend the documentary, “Crips and Bloods: Made in America”
https://www.quora.com/What-is-a-gangs-turf-and-why-do-they-fight-for-it
Another:
A gang is an interstitial group, originally formed spontaneously, and then integrated through conflict. It is characterized by the following types of behavior: meeting face to face, milling, movement through space as a unit, conflict, and planning. The result of this collective behavior is the development of tradition, unreflective internal structure, esprit de corps, solidarity, morale, group awareness, and attachment to a local territory" 1. African-American gangs began to emerge in the Los Angeles area during the 1920's, which was in concordance with the large black population in the city. The gangs in existence at this particular time in history were not territorial. On the other hand, they were "loose associations, unorganized, and rarely violent" 2. Moreover, they did not employ monikers, graffiti, or various other gang characteristics to identify themselves. Gangs of the 1920's and 1930's were composed mainly of family members and friends, and they were involved only in very limited criminal actions. In fact, the main purpose of these criminal activities was to transmit a " 'tough guy' image and to provide an easy means of obtaining money" 3.
During the 1920's and 1930's, gangs such as the "Goodlows," "Kelleys," "Magnificents," "Driver Brothers," "Boozies," and the "Bloodgetts" wandered the streets of Los Angeles. All of these gangs committed petty crimes in comparison to gangs today. The "Boozies," for example, consisted of brothers and their friends who engaged in prostitution, theft and forgery. As the 1940's approached, black gangs were beginning to grow in numbers. Gangs including the "Purple Hearts," "31st Street," and "28th Street" emerged in this decade, and their activities were very similar to those of gangs in the 20's and 30's. In addition to theft, prostitution and forgery, gangs of the 1940's were involved in extortion and gambling. "They were very effective in forcing local merchants to pay the gangsters for protection, which amounted to paying the gang not to burn the merchant's store" 4.
The 1950's witnessed the arrival of car "clubs," which included the "Low Riders," "Coasters," "Highwaymen," "Road Devils," "Businessmen," "Gladiators," "Slausons," "Rebel Rousers," "Huns," "Watts Farmers," and the "Blood Alley." These particular gangs were extremely protective of their territory, however, they were not organized very well and did not consist of many members. The activities of the gangs remained the same in relation to previous decades. Any conflicts that did arise between gangs occurred when rival gang members found themselves in an enemy's territory. As was generally the case, each gang would gather it's members together, meet in a deserted lot or park and physically fight to the end. The gang with the most people standing at the conclusion of the fight was declared the winner, and the losers would simply limp home and recover. Weapons, such as chains, knives, and bats, were used occasionally in these rival conflicts. These types of weapons are in stark contrast to the commonly used semi-automatic handguns and AK-47's in today's gang fights.
This is part of a much larger article.
https://web.stanford.edu/class/e297c/poverty_prejudice/gangcolor/lacrips.htm