How is lethal injection, hanging, firing squad, or the electric chair any more civilized than beheading? The end result is the same - a quick death for those that have committed crimes that call for capital punishment. Are you against all capital crime, or just the ones that you don't like? As for treatment of war prisoners, do you believe that we did not torture Muslims at Gitmo, or the other black sites in Europe? Do you think that US operatives have never cut off fingers to extract information? If you think that the US doesn't torture, I have some seaside property to sell you in Montana.
Religion is not the cause for war. Men using religion in their quest for power and land is the cause of war. Just like a gun cannot shoot someone without a person picking it up and pulling the trigger, a book cannot do anything until someone uses it's writings.
There is no need for justification of belief - we are discussing historical facts, and you keep confusing yourself by trying to apply your current modern beliefs with ancient times.
Since you do not seem to realize this basic concept, you should move onto the next scripture.