Well for many reasons,but to be exact,NV represents our world in a nutshell,if you can see it. Every supreme leader of our real world,be it our national politician head of countries or so called terrorist,too in a way wants peace in the end. People with no reasons to kill others,or who does that just to have a pleasure of killing basically are just pawns of people with reasons who sits on the top. Sure there methods are different,and twisted,violent but still they want the similar goal. There is just no understanding. People just raise war for many reasons,love,power,influence,etc. but in the end when they desire to control others,it's because they want to have a peace of mind. Humans in the end of a day wants that internal and eternal peace. People who don't [Like HIDAN] are just sick,and merely always pawn in the real world.
NV like our world works on perception. Nothing more or less.