Complex sentence: The Pioneer Mill, the largest, remained in operation until after World War II. But as the New England textile business moved to Southern states the Waverly mill was converted into a shoe factory in the 1940s and the Pioneer mill converted to manufacture doorbells in the 1950s.
Split into simpler sentences: The Pioneer Mill, the largest, remained in operation until after World War II, but as the New England textile business moved to Southern states. The Waverly mill was converted into a shoe factory in the 1940s, with the Pioneer mill converted to manufacture doorbells in the 1950s.