In order to learn how social groups are created in the first place, and maintained in the long run, you have to understand what is considered to be a social group. A social group is defined as the following: a social group that comprises of any number of people with a common goal or similar beliefs. In regards to politics of any nature, social groups are extremely important for the most part. Political parties, military organizations, businesses, religious congregations, charities, advocacy groups, and other organizations can be considered as social groups. Social groups can be formed for many reasons as long as the members share the same goals, ideals, beliefs, or any other similarities. However, a true social group would have some sort of cohesion instead of a group of people gathering.
Social groups are formed via the cohesion around a certain goal, ideal, belief, etc. Martial arts organizations are a good example. One can look at the two main organizations of Tae Kwon Do: International Taekwondo Federation (ITF) and World Taekwondo Federation (WTF). ITF focuses on the belief of focusing on “traditional” Tae Kwon Do while WTF focuses more on kicking techniques. Another example of martial arts as a social group would be the International Shotokan Karate Federation (ISKF), which centers around preserving and spreading the teachings of Masters Gichin Funakoshi and Masatoshi Nakayama.
On a school level, you would have your student political groups, sports teams, and school clubs. They are social groups. Student council focuses on the ideal of politics at a school level as they do various activities. The football team revolves around competitive football. The debate club revolves around the idea of becoming very good debaters.
The military is an example of a massive social group. People join for various reasons: traveling, job security, duty, and so forth. There are various reasons that keep servicemen and women together. But, the main reason that the military is formed is for the country's defense.
However, there is a dark side to this as well. Religious cults, hate groups, degenerate groups, gangs, and terrorist organizations are also considered as social groups. Not all social groups are good and not all are created equally.
One simply has to take a look at groups such as the Westboro Baptist Church, Heaven's Gate, Al-Qaeda, Crips, Bloods, MS-13, NAMBLA, and FLDS (Fundamental Latter Day Saints). Even the most radical goals and ideals can bring together people to form their own social groups. Hate and supremacy groups are no exceptions.
Creating a group can be easy or difficult due to a number of variables. However, the main trick is keeping the group in line. An eHow article on the matter gives a list of methods in maintaining such social groups: attracting like-minded individuals, building the group's identity, building a cohesive movement, and sharing common goals.
However, maintaining a group is easier said than done. Even though social groups share common goals and so forth, maintenance is the X-factor. One method might work for one social group but might not work for another social group. Group one can use positive reinforcing such as rewards to keep the group in line. Group two can use negative reinforcing such as punishments and humiliation as a means to keep the members in line. Group three can use a code of discipline to keep the members in line. Group four can use threats of expulsion to keep the members in line. In cases such as political organizations, this can be done via elections and other things to avoid in-fighting and everything else.
Remember that a company, a military, a religious organization, a special university, and so forth can be considered a social group. Depending on the group's beliefs, leadership, and infrastructure, there are numerous ways to maintain the group.