Tribalism is human nature, as social success - a key survival criteria - requires alignment.

The reason it becomes a problem is that there the only options for each "tribe" is one of two extremes, and that these are perceived so fundamentally different it is hard for people to find common grounds. When you have many more parties, you have a wider spectrum where you can have partial agreement and disagreement with much softer borders between political strongholds, and tribes can incrementally move within the spectrum without having to switch all their beliefs and ideologies from one day to the next.

Being more understanding of tribes with other ideas rather than making them villains would also help both sides in communication and political mobility.