Complex sentence: The largest percentage increases of the Dow Jones occurred during the early and mid- 1930s, but it would not return to the peak closing of September 3,1929 until November 23,1954.
Split into simpler sentences: The largest percentage increases of the Dow Jones occurred during the early and mid- 1930s. But, it would not return to the peak closing of September 3,1929 until November 23,1954.