Complex sentence: Two-thirds of a million visited in 1946,1 million in 1954,2 million by 1966,3 million in the 1980s, and 4 million in the 1990s.
Split into simpler sentences: Two-thirds of a million visited in 1946. Visitation reached 1 million in 1954,2 million by 1966,3 million in the 1980s, and 4 million in the 1990s.