The thought of a one world government is a truly revolting concept. But seeing as it looks like we're headed that direction anyhow, I might as well throw my 2 cents into the global piss pot. So here goes: A world-wide constitution would be very complex as you would have to consider Nation's right as well as state/province rights as well as personal rights. So in this context we'll use a very broad-based approach. There should be universal standards on human rights, cruel and unusual punishment and what-not. There should be Global emissions and waste standards. There should be at least basic speech and press freedom standards. No one is required to be a democracy but if that decision is made, there must be strict standards of fair election practices that everyone adheres to. All nuclear weapons must dismantled else face penalty of the strictest sanctions the world can impose. I'm sure there's other stuff too. Obviously the actual formation of such a document would take years (if not decades) to create, and I'm just making this up as I go along, so I'm I missed a thing or two. And so on.