Complex sentence: It was not until the conclave of Cardinals had gathered to elect a new Pope that Napoleon decided to bury Pope Pius VI who had died several weeks earlier, with a gaudy ceremony in an effort to gain the attention of the Catholic church.
Split into simpler sentences: It was not until the conclave of Cardinals had gathered to elect a new Pope that Napoleon decided to bury Pope Pius VI who had died several weeks earlier. He gave him a gaudy ceremony in an effort to gain the attention of the Catholic church.