Religions have been misused as tools of oppression and to obtain and maintain a power elite, for sure. The Catholic Church certainly blessed the invasions of what are now South American countries, and benefitted enormously from their looting and the massacre/oppression of indigenous peoples. But I don't think that Christian vs Muslim, or interreligious conflicts, such as Protestant vs Catholic and Shi'a vs Sunni account for nearly as many killed through political, racial and tribal conflicts.
Northern Ireland's 'sectarian strife' (a euphemism for religious war) is a weakling against the savagery of the Hutu vs Tutsi tribal massacres (When Two Tribes Go to War) in Rwanda, the various recent or modern genocides in Europe, Indonesia, the Sino-Japanese war, and all of the political (or ideological) wars that the USA has been instrumental in, bringing down one government and setting up one of its' choice by force. The Mau-Mau so-called 'freedom' movement in Kenya in the early 1950s murdered a much-publicized 100 or so whites, while over 10,000 Africans were slaughtered on tribal grounds. God knows how many have died in various tribally-driven internal wars in African countries, including those which pre-date colonialism.
We fought Argentina for the Falklands not because of religious intolerance, and Brian's admirably outlined a number of world leaders who caused the deaths of tens of millions through far from religiously-motivated actions.
It's odd, this topic, because I was mulling it over to myself recently (there being a dearth of people interested in mulling it with me), and I rather startled myself by my own conclusion that, however beastly the organized religions have been to each other and within each other, their savageries are very unlikely to exceed the death rates of those killed for other 'reasons'.
I'm quite happily areligious now, having tried hard as a child to love Christian values. I'm also quite happy for there to be any amount of belief systems, provided they don't promote false notions of superiority over others, but the idea of a born-again Christian deciding to kill a person because he's an atheist (as an example) is as illogical and pointless to me as a white man deciding to kill another because he's a Pakistani.