Complex sentence: The Sadler's Wells Royal Ballet returned to Sadler's Wells theatre in 1970, whilst continuing to tour the country, however in 1987, the company was invited to be come the resident ballet company at the Birmingham Hippodrome.
Split into simpler sentences: The Sadler's Wells Royal Ballet returned to Sadler's Wells Theatre in 1970, while continuing to tour the country. In 1987, however, the company was invited to become the resident ballet company at the Birmingham Hippodrome.