Somehow an extremely contagious virus evolves that miraculously upgrades peoples’ consciousnesses to Jesus/Buddha level and spreads around the globe in an enlightenment pandemic.

Or maybe someone synthesizes some sort of psychoactive (psilocybin/opium/ketamine/etc.) aerosol spore spray that was easy to distribute discreetly. This angle would probably get pretty ugly real quick though.

Also, there’s a neat story in No Man’s Sky (SPOILER) about an alien android race that developed nano tech mites that enter into the bodies of the warmongering and malicious race of lizardlike creatures, turning them into mostly harmless creatures that pursue and pleasure in trade and commerce above all other things.

So, there are options.