Complex sentence: Agitation Free reunited in 1998 and released "River Of Return" in 1999; then reformed in 2007 (with the 1974 line-up) for a series of concerts in Tokyo.
Split into simpler sentences: Agitation Free reunited in 1998 and released "River Of Return" in 1999. The band again reformed in 2007, with the 1974 line-up, for a series of concerts in Tokyo.