Complex sentence: When a new Loudoun County high school opened in 1997, both Broad Run and Park View were AA size again and moved down to AA in 1999, but Woodson was added to reunite it against its rival Fairfax.
Split into simpler sentences: When a new Loudoun County high school opened in 1997, they were AA size again. This was remedied in 1999 when Broad Run and Park View returned to the Northwestern, and Woodson was added to reunite it against its rival Fairfax.