The Soviet Union was very antireligious, as was Mao's China and Pol Pots' Cambodia. So are the Tamil Tigers, though I'm not sure if you can call that a regime. Can we count wars against their own populations, such as Tibet or the cultural revolution? (part of the rationale of this was to stamp out fuedal superstitions). The Soviet Union launched wars against dissidents in Czechoslovakia and Hungary, against Afghanistan in the 1980's, and aided various other military efforts worldwide. The Chinese have attacked Vietnam, India and South Korea at different times.I am curious Eckadimmock, specifically which regimes were avowedly Atheist? That have been warlike that is. Russia? Cuba?, What war did they start? We might not like their methods of running their countries or treating their people but what countries did they wage war upon (not talking about defending themselves but aggression itself). The "Cold War" doesn't count.
I don't say this is in any way caused by Atheism, but it illustrates that absence of religion does nothing in itself to promote peace.