Final answer:
Teams like Real Salt Lake and D.C. United belong to Major League Soccer (MLS), the professional soccer league in the United States.
Step-by-step explanation:
If you search for "...sports league," and find information about teams like Real Salt Lake and D.C. United, the sports league you've found is Major League Soccer (MLS). These teams are professional soccer clubs that compete in the men's professional soccer league recognized by the United States Soccer Federation. Major League Soccer operates with both Eastern and Western conferences, similar to other major sports leagues in the U.S., and continues to grow in popularity as the sport of soccer is rapidly becoming more popular in the United States.