Complex sentence: The pandemic caused by the 1918 influenza outbreak was by far the most devastating single disease outbreak in modern history killing 50 to 100 million people during an 18-month period, and killed 72 out of 80 residents in Brevig Mission in a 5 day period.
Split into simpler sentences: The pandemic caused by the 1918 influenza outbreak was by far the most devastating single disease outbreak in modern history, killing 50 to 100 million people during an 18-month period. In Brevig Mission alone, it killed 72 out of 80 residents in a 5 day period.