One of the reasons behind the fight is whenever human being feel threatened about their lives or livelihoods they prefer to protect it and they choose to fight for it, usually human beings prefer peace but when they get threatened about their lives or about their people they choose to stand for it. 

 The reasons are both simple and complicated. We're wired to defend territory and self-protect. Our minds make quick judgments.  

A series of studies found that in the workplace, people who are given lots of power but low status tend to spark an unusually high level of conflict. Put them on a task with someone else, and a "vicious cycle" of perceived insult and responses is likely to form, which can lead to arguing.