Complex sentence: Scholars of the 19th and early 20th century estimated about 2,000 persons at the time of European contact in the 15th century, but recent scholarship suggests there were no more than 500 to 700 people.
Split into simpler sentences: Scholars of the 19th and early 20th century estimated about 2,000 persons at the time of European contact in the 15th century. Recent scholarship suggests there were no more than 500 to 700 people.