Why are the Cowboys considered "America's Team"?

Where did the tag of "America's Team" come from? Wouldn't it make more sense for the Patriots to be America's team. If it weren't for the actions of great Patriots like Thomas Jefferson, George Washington, Paul Revere and John Han where would we be today? I'm not discounting the bravery or work ethic of Cowboys or their role in American history. America became America with the unselfish acts of a few great Patriots not great Cowboys. Maybe Cowboy fans should rethink this or maybe not, its just a question.