WAY back in the 60's. It only applies to US players, Canadian players, and Puerto Ricans.
It used to only apply to Americans and maybe Canadians. I know that they added Puerto Ricans later.
I'm not sure what you are asking about as far as advantage. If you're talking about more money, not necessarily. Most foreign players get signed for very, very little. Americans have the advantage of using the draft for leverage and they get more money even though they can only negotiate with one team.
Japanese players who are posted and such- yes, they get large salaries, but those players are basically expected to be immediate impact type guys and can go to MLB right away. There's a little bit smaller risk with those players compared to players from other countries.
Stephen Strasburg signed a contract for 30 million or so after being drafted, which is the record for an American player- I think his bonus was 15 million. The Rangers just signed Nomar Mazara to a 5 million dollar bonus, which is a record bonus for an international player.
And missouridawg- it's not just the small market owner's that want an international draft. All the owners and the players want an international draft. It doesn't have anything to do with teams like the Yankees hording players- because they're not. It's about teams having control of players- and you're also going to see a slotting system which will take away the draftee's negotiating power. It will be pretty much- "You were drafted in the 10th round. This is what you will get. You option is to sign or go to college or go play Indy ball." There will be no more "signing above slot". It's about teams saving money on the ownership end. The players are also for it because there are players that will say- "Hey, I've been in MLB for 8 years, and have had a solid career. This guy has zero MLB experience, and you have no idea if he's going to pan out or not, and he's getting more than me." Basically, you can thank Scott Boras for all of the draft changes.
As far as college baseball- it's going to help MSU and everyone else out. Our recruits are going to know exactly how much they will be offered on day one, and we will have a better idea of who will sign or not. Adding international players is going to push most players down in the draft as well- which is good for us. You will probably see more talent in college baseball and more guys staying for the senior year than ever.