Complex sentence: Large-scale festivals of Japanese culture were held in the U.K. in 1981 and 1991, and in 1998 a reciprocal event, the UK98 festival, was held with the cooperation of the association to introduce British culture to Japan.
Split into simpler sentences: Large-scale festivals of Japanese culture were held in the U.K. in 1981 and 1991. In 1998, a reciprocal event, the UK98 festival, was held with the cooperation of the association to introduce British culture to Japan.