Where should one start? How far back should we go?
I mean, a basic primer is the entire Heather Cox Richardson thread, which stands at almost 3000 posts. Better yet, a strong foundation in US and world history along with a helping of US government and political science.
The problem with asking for short answers to these questions is that it assumes those having the conversation are starting from the same baseline of background information. And nothing is quite as frustrating as being asked for a short answer only to have the other party in the conversation demand more and more information to back up the assertions until it becomes an AP US History course.