Well, we have 1200 years of Muslim history to look at to see what might be the warlike effects of excess males due to polygamy. Admittedly there are other factors at play in that case, but are you completely discounting it? If so, why?
Actually, polygamy was a response to excess females - as Muhammad's cohorts died off, he had their widows married to those who remained standing. The problem of excess females led to an ever-widening spiral of conquest for loot, as the men joining his army died, the remaining men had to take on the widows of the dead, thereby necessitating the acquisition of yet more loot. Note that the female surplus problem was severely aggravated by the practice of massacring male captives.