English history and common law (Wikipedia)  The concept of a universal militia originated in England The requirement that subjects keep and bear arms for military duty dates back to at least the 12th century when King Henry II, in the Assize of Arms. In the English feudal system of that time, there were relatively few landowners, most of whom owed their title to land through their obligations to the King who they were obliged to defend. Most of the population at that time were peasant farmers or "serfs" paying rent in the form of a share of the land granted to them to work. Serfs were thus tied labour and were not permitted to leave the service of the Lord of his manor. About ten percent of the population were "freemen", a class of person in the feudal system who were not tied to the land in the same way as the serfs and who paid rent in the form of money. The Assize of Arms obliged certain of these "freemen" to bear arms for defense of the monarchy, thus considerably extending the numbers of persons equipped to do so.

In response to complaints that local people were reluctant to take up arms to enforce justice for strangers, The Statute of Winchester of 1285 (13 Edw. I) declared that each district or hundred would be held responsible for unsolved crimes. Each man was to keep arms to take part in the hue and cry when necessary. The reason for such a requirement was that without a regular army and police force (which was not established until 1829), it was the duty of certain men to keep watch and ward at night to capture and confront suspicious persons. Every subject had an obligation to protect the king’s peace and assist in the suppression of riots.