as a conquest excuse, yes, it did spread through Europe as a carrier or co-exister with western civilization. But Western civilization existed before Christianity. Then Greco-Roman gods and beliefs mingled with Zoroastrianism, Judaism, and other Middle Eastern belief systems to produce various early forms of Xtianity. The Roman Catholic one dominated western Europe, with an influence from the others.
I think that people who complain about religion causing wars and genocides often have cause and effect reversed. Many times, religions are genuine expressions of or spiritual searches for personal meaning and guidance on living with others. Political leaders can use religion as an excuse to carry out political agendas.
I see religion in many layers. The most obvious layer is literal, linear, and often historical. It carries cause-effect beliefs that are somewhat magical. Say the right prayers, offer the right sacrifice, and all will be well. When tge formula doesn't work, people find excuses to preserve their perspective, or turn against former beliefs. It's often a child's view of religion that people outgrow and then they reject all faith as childish.
Another layer of religion is an expression of psychological, social, and personal "truths" or truisms about life, expressed in story form for meaning and memory. We recognize both higher and baser sides to human nature. Genesis expresses this metaphorically as man being formed from the dust of the earth and given life through the breath of God. Tribal religions in the Americas, Africa, and Asia have legends or sacred stories about people's relationships to each other and nature that represent the same kind of metaphorical meaning, but we oftwn miss that because we don't understand the spefic symbols in other societies.
A still deeper level offers guidelines for not only interactions with each other, but for individual and social spiritual growth and development that brings insights, inner peace, moral values beyond simple obedience to rules.
There are many more approaches to religion and layers of understanding involved than I want to get into right now. People find for themselves whatever level of belief or disbelief suits them.
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