Complex sentence: It was not until 1924 that the industry recovered, reaching 2,700 tons in 1932 and a record 4,000 tons in 1935, mainly African production in the lower Shire valley, as output from European estates became insignificant.
Split into simpler sentences: It was not until 1924 that the industry recovered, reaching 2,700 tons in 1932 and a record of 4,000 tons exported in 1935. This was mainly African production in the lower Shire valley, as output from European estates became insignificant.