Complex sentence: In 1916, Bethune became president of the Florida Federation and in two decades, under her leadership, the Federation grew to include more than 60 clubs, in at least 20 cities, with at least 13 members in each.
Split into simpler sentences: In 1916, Bethune became president of the Florida Federation. During the next two decades under her leadership, the Federation grew to include more than 60 clubs, in at least 20 cities, with at least 13 members in each.