I think another cause of division is that the general population are taking some of their cues from politicians. The general population itself are becoming politicized in that we're engaging in the same behavior that politicians tend to engage in. It's one thing to have a political view, but it's another thing to engage in political behavior, and unfortunately the latter is happening.
However, one key difference between us and politicians is that the political behavior of politicians tends to be contrived. In other words, they know how to cause divide, and find ways to use it against their opponent in order to win an election. In our case (general population), political behavior is likely done by a lot of people naturally (since we're not running for election) thinking that that is the way to go. As an example of all of this, we can say that politicians may deliberately inject race, morality, or some other emotive-evoking factor into discussion just to inflame the issue and create divisions. We just play out the result of that by dividing over issues, labelling each other racist, bigots, evil, etc. I can't call the latter group doing it contrived because I've seen friends engage in political behavior with other friends and even with family.
I think one way we can keep from dividing over differing political views is to remember our similar interests starting at the basic level. We all want good jobs, a good house, a good life, etc. We might also agree on a lot of moral standards, family values, etc. Don't define or judge each other based only on a view, esp. when views are not illegal unless it involves threats of harm.
* I define political behavior as mostly the negative or underhanded behaviors/tactics that politicians tend to engage in, like engaging in spin, demeaning their opponents, engaging in inflammatory rhetoric, moral posturing, etc.
