Genealogy societies form in order to pool resources, time and energy among a group of people researching similar people from the past. Most genealogy societies are formed to serve the people of a certain geographic location and their descendents. These are divided up into a variety of sizes. Some focus on a small local area such a town, parish, or county. Others focus on a single state or region. Still others focus on the entire country or group of countries.
A genealogy society does not have to be located in or even anywhere near the area it hopes to serve, but it does help. When the society is located near the geographic region it serves, there will be other resources available to them, as well as knowledgeable historians who can provide information to researchers.
Geographic regions are the only boundaries that prompt groups to form and research en masse. Those whose ancestors share a common history, such as the Mayflower Society can form a group from the descendants of those who came to America on the Mayflower. Members will undoubtedly come from every corner of the country, and perhaps the world.
Descendants of ethnic or religious groups such as Hungarian Jews or Huguenots from France also band together to help each other in their search for family history. There are also religious groups today that incorporate family history into their religion and that offer a wealth of genealogical information to the public.
Whatever the boundary, ethnic group, religion, or historical event, you can find information about them on the internet. A quick search for "genealogy societies" will yield more information in a few seconds than a person can process in several days.