Why has civility nearly disappeared in our culture, and how can we encourage its return?

The culture in the United States has become very divided on so many issues, and the ability to have a civil discussion seems to have almost disappeared. People holding an opposite perspective from our own are often demonized and viewed as the enemy. Discussions often degenerate into name-calling and belittling and personal attacks. How can we encourage a return to civility, so that we can all come together and discuss the issues in a reasonable and calm manner, even though we might hold drastically differing positions on those issues?