The Contradiction of a Religious War

I've always speculated on people like Abraham and Jesus and Muhammad. I wonder, when they preached of peace and love that they truly expected all of their followers to go out and brutally kill their enemies. Was "you shall not commit murder" codeword for "kill people over the slight differences, making sure to ignore the vast similarities?" Was "you shall not covet your neighbor's house" a subliminal message meaning "start the crusades in a quest to get 'your' land back?"