So why is the Bible and the Christian religion full of glorified violence and Bible believers so quick to defend that violence as justified?
I believe that part of the answer to this question is "land." If you consult the map of the "Old-Testament Bible lands" below...
...you should see that Israel was located between Egypt to the south-west and Mesopotamia to the north-east. As warring factions between these parts of the world vied for supremacy, they needed to control that little patch of land that was to become Israel. So the Hebrews suffered continual attacks as their land was taken by conquest again and again by these greater powers.
Needless to say, the Jews were not happy with their lot. From Babylon to the "whore of Babylon," the Jews understandably felt great anger against those nations that enslaved them and occupied their homeland. Since they could not realistically drive off most of these invaders by the sword, they turned to "the word." The "word" was presumably the "sword" of their god. By writing of their god driving off these invading nations using his magical powers, the Jews hoped that not only would they gain their freedom but that they would gain that freedom safely relaxing as their god did most of the work.
So that's one of the main reasons the Bible is full of violence. The Jews and later on Christians were "writing their salvation into history" as they imagined their god freeing them from their oppressors.
But there's a bit more to what causes Christian violence and religious violence in general. People, and not just the religious, need not just land but other resources to survive and have hope for the future. Seeing that these resources may be scarce or thought to be scarce, they may well go to war over those resources if need be.
Note that in contrast to land, resources need not be "real." Resources can be and often are created in the imagination. In order to attract converts, resources like "salvation" need to be scarce and exclusively offered by one and only one religious faith. So to attain salvation, not just any religion or any Christ will do. One must put one's faith in the "true" Christ and the "true religion."
So who is the "true Christ," and what religion is the "true religion"? Considering that religion can be imagined any way you wish, any religion can claim to be true and to worship the one true Christ while denouncing all other religions and Christs as "false."
These claims of salvation as "a scarce resource" exclusively offered by one religion can lead to violence. Just like people may turn to violence over a real resource like land, they might very well turn to violence over an imaginary resource like salvation if they feel their salvation is threatened by the "false" beliefs of other faiths.
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