I think this idea is rather clear
when you consider the personality
of the God
that is believed
by the society
where the religion
Take the Hebrew god, YHWH, for example. The Hebrews of the time of the Torah were a very warlike people, living in a very violent area. Thus, they had a very cruel and vicious god, who killed people en masse left and right, ordered a number of genocides, and sent a bear to maul children just for making fun of a priest. Their god was created after the type of life they knew.
Any violent people would believe in violent gods, as they wouldn't want to feel like they were disobeying their god by believing a god of peace. And of course there would be a tendency for the beliefs in the violent gods to persevere, as they'd overrun any peaceful ones and eliminate them.
Of course, then again, it could work the other way also, as a cruel, violent god who made people in his image would make them cruel and violent also...