Complex sentence: In the late 1890s, Southwest Ohio was the heart of the US flaxseed growing area, and there were as many as 13 linseed oil mills in Piqua, where the flaxseed was "crushed" to extract the vegetable oil, named linseed oil.
Split into simpler sentences: In the late 1890s, Southwest Ohio was the heart of the US flaxseed growing area. There were some 13 linseed oil mills in Piqua, where the flaxseed was "crushed" to extract the vegetable oil, named linseed oil.