individual belief – no… (unless they are criminally insane and use “messages from god” as an excuse for committing violence)
organised religion – in many cases yes; where someone has set themselves up as a religious leader and encouraging others to follow the word of deities and take actions in their name – in many cases this is just a way of reinforcing social and power structures.
In ancient times a church. temple or mosque would have been set up by people with power and resources and provided a lot of resources and services that today the public sector provides (such as social care and care of the sick), but is usually open as a public building on condition that you give some support or respect to the beliefs of the people who run it. It also contains resources worth guarding such as religious artefacts made out of precious metal, good quality stone and as such is always subject to the risk of theft and often has to be defended, and people have a group/gang mentality anyway.
The actual nature of the gods or the location in the world where the followers are does not matter – more the belief that their community or religion better than anyone elses idea is what spurs people to fight crusades / jihads.
Also there were disputes between the congregrations of rival churches in different villages; often fights at border areas etc. One of the local history sites I visit mentions how such a dispute (in the 1700s/1800s) in East Anglia escalated into accusations of sexual crimes by the vicar, fights in church and bodies being dug up out of the graveyard and buried elsewhere!
Of course (speaking for Britain) today your local Anglican vicar does not today encourage his flock to physically attack members of rival organisations (although even today there is violence between rival Christian groups in the disputed territory of Northern Ireland) but that is only because they have a position of power and influence within the Government.
If you read British Acts of Parliament (laws) you will still see references to the Lords Spiritual (the heads of the Church of England) as well as the Lords Temporal (the old fogeys in the House of Lords), the church and state here still have many links…
I have an interest in history and for hundreds of years this country was awash with blood due to religious disputes where Protestants and Catholics fought one another; it is literally only in very recent times (I would say the last 30-40 years!) that there has been more religious tolerance in Great Britain.
Only a few hundred years ago in Britain people were being burnt alive by mobs for having the wrong religious beliefs; even for supporting the “wrong form” of Christianity.
