Do religious dogmas have to be so divisive?

The short answer to this seemingly simple question is ‘No, they do not have to be divisive.’ But, are religious dogmas divisive, or have they been divisive – as between peoples sharing a geographical location or living in close proximity to one another? For the most part – throughout known history – would the answer be a decisive ‘No’? Having regard to the colonial experience, when the buccaneering trader was accompanied by a soldier on one side and a priest on the other side, the invader’s religion was divisive (if not deadly)! Look at what happened when the conquistadores arrived in the Americas.
Yet, colonial subject peoples were, as least within my experience in a multi-ethnic environment, tolerant of one another’s religion and associated culture. Religion was lived and not talked about; there was mutual acceptance. Is that a feature of non-combative Asian cultures (which then included Muslim Malay culture)?
In reality, from a global point of view, an ambitious ruler (or a greedy tribal chief) could have used a perceived difference (self-chosen) between his people’s god and the god of those whose lands and other assets he covets, in order to ‘smite’ those others. Whether or not he is a priest-king, injunctions from a powerful priesthood or a ‘Good Book’ would provide necessary authority to act.
Highlighted cultural differences as between these peoples could also provide the necessary excuse for the intended butchery. A chosen cultural difference may be a difference in theology or dogma.
One has only to note what is happening in the Middle East. Is not religious dogma associated with the combatants to a substantial degree, while the primary aim is obviously control of oil or other asset-rich lands? Since religious beliefs cannot be divorced from other motives, how much ‘collateral damage’ is tolerable? How many innocents have to be killed, maimed, or starved in the name of religion or its ghostly underlay, democracy?