Do you live in the United States? If you do then unfortunately you are witnessing how it happens.
It begins in most cases with hatred. There are two sides to an issue. Men of good faith cannot listen to someone with the opposite point of view.
I grew up in an era where the left and right would compromise with each other. The debate was often furious but when it ended, men of good intentions knew that the battle was over. I don't think that's true any longer. I think the battle just keeps on going with new issues to be fought over.