Complex sentence: Between 1900 and 2000 CE the population of the world increased by 277% (fourfold-from 1.5 billion to 6 billion); the European component increased by 124%, and the remainder by 349%.
Split into simpler sentences: Between 1900 and 2000 CE the population of the world increased by 277%, a fourfold increase from 1.5 billion to 6 billion. The European component increased by 124%, and the remainder by 349%.