Oprah Magazine provides a good intro to a "new field called peace psychology" -- except for its title ("Let's not fight!") and its opening sentence ("Imagine a world without conflict.").
A world without conflict would be a boring place. Conflict is necessary and good. It's unrealistic to presume that all people will share the same perspective, the same approach, the same desires, the same goals. And as long as there is more than one human on the planet, there will always be fighting -- and that's not a bad thing, either. Fighting is necessary and good.
It's how we fight, and how we resolve conflict, that matters. Anticipating inevitable disagreements, whether between spouses or neighbors or nations, and learning how to peacefully resolve them (without violence or litigation) is the admirable goal to which we should all aspire. And in fact the article outlines invaluable methods of constructive dispute resolution worth adopting and modeling for the next generation.
So go ahead and fight! Just remember to fight nicely.