According to me? Nothing. If I have to be quite honest I'd say that war has a lot to do with a male ego. Look throughout the centuries, men have started wars over the most trivial of things. Okay I'm sure it wasn't trivial at the time and I'm sure they thought they had very good reasons. But hey, emotions and ego's were running high at the time. We are all guilty of that. Wars aren't only shooting, killing and fighting. There are wars waged in each of our lives almost everyday, or at least some times in life. These wars include fighting with our loved ones, friends and family. These wars can tear people apart. These wars, just like their greater counterparts, usually revolve around love, hate, religion, differences in opinion and such.
Everything can be sorted out. One way or another. Even if you agree to disagree. Apologize. Talk. Share your feelings. Speak the truth. Even if it might hurt. Don't lie.