Holy and War an Oxymoron?

Holy and War could never be a word that were put together, they're are just opposites, when someone says holy, they think of peace and something being very sacred, and when someone says war, they think of anger, conflict and violence. They belong to two completely different moods too, a person would only go to a holy place when they want help or when they want to thank god. However, a person only wants to go into war when they want to finish a conflict, or colonize the other side. Also, I have noticed that in almost every religious temple, there is this atmosphere that is very quiet, and soothing. Whereas when in a war( I infer from the movies), that it is very loud, rough and forceful. It is clear that these word are just too different to be put together.

To answer the second question, since almost every religion prevents war, why are the causes of most wars religion? Let me start with how the not every religion reclines from war, Islam, however, promotes war when it is in a deadly position, and I think, deep down almost every religion thinks the same, and why shouldn't they, if your religion is in a state where it might become extinct, you would have to fight back for what you believe is right. Another reason to why most causes of war are religion would be the fact every religion believes in different facts, they get too caught up with the little details that they forget that the overall fact is the same, like in Islam, Shina's and Sunni's, they both believe in the same god, yet the main causes of war in Iraq are the Sunni's and the Shina's. This shows that many religions are forced to fight with one another to save their their religions, or to stick to their facts or beliefs.