Online communities give people another way to feel part of a tribe. Very small niches of people can find each other, connect and share online. In the past it was really only convenient to network with people you were often in the same geographic area as. It also took time and money to organize people, so only the groups with large enough bases were usually successful creating communities. The internet has reduced the barriers for connecting and organizing to almost nothing. Communities can be and are being created about anything you can imagine, every day online. People join online communities to connect with people who they don't have the chance to find or socialize with offline.