Religion, whatever we might think of it, has been probably the most potent force for mobilizing people the world has ever seen.
Perhaps the greatest example in human history of the quickest, most lethal mobilization of a people is Hitler's Nazi State. It is not related to religion, but was a combination of factors - psychological, economical, and political.
When the appropriate climate exists and the right man positions himself to exploit the needs of a people experiencing a desire to regain security and be "liberated" from the aforementioned stress factors, you have the making of a potent, formidable force, WITHOUT religion playing a predominate role.
Hitler, although a morally depraved monster, was a master manipulator that was able to seduce the masses with his "politics of exclusion."
Hitler wrote..,
"To begin with, Judaism is definitely a racial and not a religious group...
The result of which is that a non-German race lives among us with its own feelings, thoughts and aspirations, while having all the same rights as we do."
The Versailles Treaty left Germany in economic ruin. It crippled future growth potential and left the people of Germany in a situation of economic desperation. Once a people with great national pride, they suddenly found themselves in a position of miserable desperation.
Hitler was in love with militarism and his personal "Mein Kampf" that he was able to psychologically transfer to a desperate people. In Mein Kampf, Hitler wrote Vienna was...,
"the hardest though most thorough school in my life" in which he obtained "the foundations for a philosophy in general and a political view in particular which later I only needed to supplement in detail, but which never left me"
World War I also helped shape his character and military value system. His usage of war propaganda was also a key factor.
We don't need a further review of history here. Most of us are familiar with the monstrous crimes committed against a race of people, by a people, indoctrinated into a racial and political ideology of superiority. The war waged was not a "Our leader was raised as a Catholic and you aren't Catholic, therefor you must die!" war.
Although there are certain individuals who are satisfied with a superficial analysis of this event and will curtail their analysis when they find a word like "Catholic" in the record, the Nazi movement was the greatest example of the mobilization of people to commit atrocities unrelated to religious tenants. I'm sure there are more examples out there to consider.