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Two of the most prominent teams in the second tier of college football will be moving up, as Georgia Southern and Appalachian State are leaving the FCS' Southern Conference for the Sun Belt of the FBS, a source tells SB Nation's Steven Godfrey. Godfrey reports GSU will make the full move in 2015, with a transitional season in 2014 and no change to its 2013 schedule. [Update: CBS Sports' Dennis Dodd reports Idaho and New Mexico State will also join, as football-only members, in 2014.]

The Sun Belt wanted to bring in existing rivals, and the relationship between App State and Southern intrigued the conference, according to a source.

The Winston-Salem Journal's Tommy Bowman reported earlier Monday that App State will announce its move this week (Georgia Southern also has a presser scheduled for Wednesday):

Appalachian State will accept an invitation to join the Sun Belt Conference this week, probably on Wednesday, according to a source at ASU — Tommy Bowman (@AppTrailWSJ) March 25, 2013

There's no doubting that these programs have proven themselves at the FCS level. Georgia Southern has won six national championships, Appalachian State won three from 2005-2007, and, as most college football fans know, shocked the sport by knocking off Michigan in the 2007 season opener. It was already well known that Georgia Southern was interested in a move up -- it'd approved the move back in September -- and the move was thought to be likely for the Mountaineers as well.

As for further Sun Belt expansion, SB Nation's Jason Kirk was told by a source in February that James Madison, Jacksonville State, UT-Chattanooga, Idaho and New Mexico State have been considered, likely among others.

The CAA's Georgia State is already moving up to the Sun Belt after three seasons of football, while the SoCon could look to new program Kennesaw State to retain a presence in Georgia.

Thus, the current state of conference realignment: