There would still be war ... because war is about resources.   Abolishing religion would just change the overt pretext on which the war was started.

Indeed, the demise of religion could lead to more conflict than we currenly experience.  If this life is all there is, you might as well go all out to get the best for yourself and your descendents.  Removing the promise of "wealth" to come after death makes the stakes higher now for those currently content to languish near the bottom of the heap (in terms of living conditions, access to food, etc), surely?  

Humans cannot ever live in peace because we are programmed to compete for survival.  That's a given that cannot be changed.  Those who live in a utopia of plenty get bored very quickly.  We need to strive and we need novelty.  This leads to good (the invention of antibiotics, say) and bad (wielding oppresive power over others).