Wars and violence have always occur through certain reason. The reason isn't very simple, it is far more complex, especially knowing the consequences of war or violence. Before anything happens, something must have build up. A war or violence is like a volcanic eruption after it has reached the limit of pressure. In the past, holy war was caused by Christianity's origin and artifact, was at the hands of the Muslim. This led the Crusaders to launch an attack towards the Muslim. Their aim was Jerusalem, the holy city, origin of Christ. Jesus was born in Bethlehem, however it was written that Bethlehem is in the land of Jerusalem. This is not to confuse when I said origin of Christ being Jerusalem.
The freedom fighters or guerrilla fighters have their own reason that led them to this last resort. They are, what we call terrorist, nowadays. Their reason is usually revenge rather than victory. As people were in depression, usually done by foreign intervention, most cases were by US. They needed a common cause to unify the people. Thus led to acts of terrorism. Actually terrorism no longer involves fighting for freedom or anything, as it hardly damages US forces as to the extent of forcing them to retreat. In fact, most bombs that exploded in Afghanistan damages the locals more than the US forces, even though it was aimed towards them. As they used the time-based bomb, most of the time they missed the US army.
Regardless of what it is, most war or violence has deep reason. Noone will declare war that easily unless they're desperate for something. It can be land, wealth, religion, or resources. Some seek glory, however those were in the past. In modern times, with international law and order, war is no longer due to ambitions of world invasion, it is rather due to different ideology, such as democratics against communism.

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