The problem with the analysis re: Marijuana is that it appears to leave out the anti-drug treaties we've signed with other UN members. As I understand it, federal legalization is a nonstarter w/r/t that agreement.
Nothing will happen to the US if it abandons those treaties. It'll be a blip in the news for one day, as a few grumbles are heard. Other than that, what you'll hear is mostly cheering and celebrating.
Other countries will take it as a cue that the global war on drugs the US has been prosecuting is now over, and they will begin legalizing (this is already underway). It's no longer a question of if; at this point nothing will stop the inevitable rolling back of the war on drugs, the momentum is overwhelming.