Complex sentence: Here he played an important role in the Bjelovar rebellion of 8 April that year when, after the revolt by Croats in the Royal Yugoslav Army during the early days of invasion of Yugoslavia, he declared the "resurrection of the Croatian state".
Split into simpler sentences: Here he played an important role in the Bjelovar rebellion of 8 April that year. After the revolt by Croats in the Royal Yugoslavia army he declared the "resurrection of the Croatian state".