... don't seem much different from wars over anything else.
Continuing on with Churchill's A History of the English Speaking Peoples, I'm into the reign of Queen Elizabeth where the wars between England, France and Spain were indeed Protestant vs. Catholic. However, the level of violence doesn't seem any different from that seen during the Hundred Years War where everyone was Catholic. Dittos for the wars between the Romans and the Britons or the invasions of the Vikings. The intrigue and plotting and scheming is the same regardless of the putative reason for war.
Maybe humans are just aggressive, selfish creatures by nature.