it wont happpen because the government wont be able to tax it. everyone could grow thier own. thats why tabacco is legal and marijuana isnt, THE TAX MAN
if one country legalizes it then the other nations will have to follow suit. it could possably happen in like the euro zone with several countrys at once, but other countrys would not be pleased, get my drift man.
i say just at least start off by making it legal for medical use like in cali. i watched a 60 minutes that was about california marijuana clubs and it doesnt take shit to get a medical card. if we can get the entire usa to be at the point cali is at then we can go from there and move to the next step.