Original: Though founded in 1887 , under Jack Hyles ' leadership from 1959 2001 it became one of the megachurches in the United States and during the 1970s had the highest Sunday school attendance of any church in the world .
Simplified: It was under Jack Hyles ' leadership from 1959-2001 that it became a megachurch , one of the first in the United States , with a steady weekly attendance of around 20,000 .