Complex sentence: Indian historian K.S. Lal claimed the loss of populations due to medieval invasions in India, claiming that the population of the Indian subcontinent decreased by about 80 million between 1000 AD and 1500 AD, by the end of Delhi Sultanate.
Split into simpler sentences: Indian historian K.S. Lal claimed that loss of populations due to medieval invasions on India. He states that the population of Indian subcontinet decreased by about 80 million by the end of Delhi Sultanate.