Paul W. answered 04/09/19
Dedicated to Achieving Student Success in History, Government, Culture
Your inquiry contains two different questions. Whether or not cultures / civilizations that practice polytheistic Faiths are less likely to launch wars than those that practice a monotheistic Faith is different from whether or not cultures / civilizations that practice polytheistic Faiths are less likely to initiate wars due to religious motives than those that practice a monotheistic Faith.
First, how does one determine what constitutes a religious war? Do wars that involve conflict between different cultures / civilizations or different groups within a civilization that happen to practice different religions (or different versions of the same religion) constitute religious wars? Even if one or both of the opposing sides claim that a war was being waged due to religious differences, the actual motives may be different. Consider how the European wars of colonial conquest in Africa in the 19th century were presented as serving the purpose of promoting civilization (specifically Western Christian civilization), when in fact they were driven by economic and strategic interests.
In any case, the distinction between supposedly religious wars and wars that aren't supposedly motivated by religion seems irrelevant. The fact is that cultures / civilizations that practice polytheistic Faiths don't appear to be any more peaceful that those that practice monotheistic Faiths. Aside from the Jews, virtually all of the Ancient civilizations - Egyptians, Sumerians, Babylonians, Hittites, Assyrians, Persians, Celts, Greeks, Carthaginians, and Romans (to name but a few) - both practiced polytheistic Faiths and waged war almost constantly. The Hindu kingdoms throughout the history of India waged war on one another; empires rose and fell. Similarly, the civilizations of the Pre-Colombian Americas - the Aztecs, Mayas, and Incas (among others) - both practiced polytheistic Faiths and repeatedly waged war.
The fact is that war is not exclusively or predominantly a polytheistic, monotheistic or atheistic problem, it's a human problem, regardless of religious persuasion.