Complex sentence: The band's first concert tour was in 1999, when they toured the United States with an annual festival featuring live performances by various heavy metal bands called Ozzfest, which was founded by Ozzy Osbourne and his wife Sharon Osbourne in 1996.
Split into simpler sentences: The band's first concert tour was in 1999, when they toured the United States with an annual festival featuring live performances by various heavy metal bands. The festival was called Ozzfest, which was founded by Ozzy Osbourne and his wife Sharon Osbourne in 1996.