Complex sentence: Bushfires in Victoria kill 173 people in what are not only the nation's worst ever bushfires, surpassing the record set by Ash Wednesday in 1983, but also the nation's worst peacetime disaster since Cyclone Mahina in 1899.
Split into simpler sentences: Bushfires in Victoria kill 173 people in what are not only the nation's worst ever bushfires, surpassing the record set by Ash Wednesday in 1983. Also the nation's worst peacetime disaster since Cyclone Mahina in 1899.