Complex sentence: The development of Jarun began at the end of 1970s when it was merely a village with building of apartment blocks, and especially in 1987 due to the building of the sport and leisure center (because of the Universiade in Zagreb the same year).
Split into simpler sentences: The development of Jarun began at the end of the 1970s when it was merely a village, with the building of apartment blocks. Development increased in 1987 due to the building of the sport and leisure center (because of the Universiade in Zagreb the same year).