Complex sentence: From the 16th century onwards, the Cotswolds were the centre of the world's woollen industry, but by the late 18th century this dominance was waning with the growth of the cotton mills of Lancashire and Yorkshire.
Split into simpler sentences: From the 16th century onwards, the Cotswolds had become the centre of the worlds woollen industry. But by the late 18th century this dominance was greatly in wane, with the growth of the cotton mills of Lancashire and Yorkshire.