Who made you in charge?

In early history, and by that I mean before the 12th century, generally there were small units or groups of families and communities. Because these family units were so small there was not a real need for formal police.  However the world started to change and these small units grew. Because of this the Frankpledge System was created. The Frankpledge system was an informal police group that was assigned to a group of twenty families or so. If there happened to be a dispute within that group then the Frankpledge System would take effect and the leaders would deal with the issue. However in the 12th century the members of this group were not enforcing the laws and failed to do their job. This caused the need for public policing. By the late 13th and 14th century a new system emerged. It was called the "Watch System". It was one of the first formal police forces. In the early development of the United States Europe's criminal justice system highly influenced the United States policing system. In the 19th century, laws were different from state to state. The growth of population (Think Urbanization: crime rates went up, riots, etc) caused the need for a formal police system. Besides the formal police, vigilantism, was and still exists today. Vigilantism is a person who decides to "police" themselves. They take the law into their own hands and do what they deem necessary. The dangers of vigilantism are valid because the fact that most of these people are not professionally trained and do not follow regular procedure. They also may interpret the law in different ways and take punishment into their own hands. Modern day vigilantism is for example the minutemen who police the United States-Mexico border. Some are regular people with no training and others are war veterans with a different type of training for the job. Many of these people carry licenses to carry guns, pepper spray, a baton, or other equipment. How would society be without formal policing?  What do you think of vigilantism? Are there any dangers to this practice?