Why would someone start a war?

The human race always seems to be at war somewhere in the world.  So often wars bring pain and suffering to both sides, yet we seem to find reasons to go to war over and over again.  Are we just violent creatures who can't help ourselves?

We usually find a reason to start the violence.  Here are some of the reasons people seem to find for starting or joining a war:

1. They see the other side as evil and they feel a moral obligation to destroy them. 
2. They believe you have a moral cause that must be advanced.  
3. They see a benefit to winning, and they think your chances of winning are great enough to justify the risk
4. They fear someone else will start a war against them, and they think it is better to have the first strike.
5. They see a risk in the world and ythey believe the only way or best way to eliminate the risk is war.
6. They believe that if they take aggressive action, there will be no resistance and there will be no war.
7. They see the current situation is so bad, that they think taking a risk of losing a war is better than doing nothing.  People who feel oppressed may do this.
8. A sociopath could enjoy violence, pain, and suffering.
9. Revenge.
10. They feel obliged to declare war because of alliances and agreements.
11. They have a desire for power and conquest.