You are allowed to go back in time and leave one core rulebook among the ancient people's of the world and all games...

You are allowed to go back in time and leave one core rulebook among the ancient people's of the world and all games, religion, artwork, and history will spin off from that one rulebook.

What book is it?

FATAL

Spelljammer

The pursuit of space flight is now the primary ambition of Humanity.

Lands of Luste

Not one that technically exists, but... Paladin, the Redemption.

It would be a WoD book, so there would be heavy emphasis on lore and the messages therein.

The underlying message? The world sucks, but you can make it a better place with empathy, compassion, and healing.

I think that Humanity would have the greatest benefit on trying to live the modern paladin ideals. Not because some higher power wills it, but because your very existence in this world demands it of you.

Maid RPG.

I'd leave Eclipse Phase just to fuck with them.

Paranoia.

Dungeons: the Dragoning 40k 7th Edition.

The fate of man is to be AWESOME.

Only War.

Pic related.

"Core rulebook" you say?
Id leave the Old Testament then, just to fuck with people.

GURPS

D&D4e

MYFAROG

Dark Heresy
Fear what could've been

LOTFP

Can I use a rules-light system in place of a core rulebook? I'm mildly interested in seeing what Everyone is John would produce.

It is too simple to be argued, debated and fought over for rule interpretation.

It won't do anything special at all.

Fun game though.

GURPS Vehicles.
They can learn the principles of automation, and also get the greatest game supplement ever designed by man as a sweet bonus.

So the Bible

> This user gets it