Complex sentence: On the opposite bank of the River Paraguay begins the area known as the Gran Chaco, with a different, hot, semi-arid climate, now part of Argentina, but in dispute in those days, and uninhabited by none except the fierce Toba Amerindians.
Split into simpler sentences: On the opposite bank of the River Paraguay begins the area known as the Gran Chaco, with a different, hot, semi-arid climate. The opposite bank, now part of Argentina, but in dispute in those days, was uninhabited by none except the fierce Toba Amerindians.