From 1996 to 1999, all American players graduating college were entered into the MLS College Draft, and were eligible to be selected by all Major League Soccer teams. Players who had already graduated from college were entered into a separate MLS Supplemental Draft. The division between the two was eliminated in 2000, when they were combined into a single MLS SuperDraft.
List of College Drafts:
References
MLS College Draft Wikipedia(Text) CC BY-SA