Complex sentence: Argentine troops killed more than a thousand Indians and displaced over fifteen thousand more from their land, which European settlers turned into a breadbasket that made Argentina an agricultural superpower in the early 20th century.
Split into simpler sentences: Argentine troops killed more than a thousand Indians and displaced over 15,000 more from their traditional lands. Ethnic European settlers developed the lands for agriculture, turning it into a breadbasket that made Argentina an agricultural superpower in the early 20th century.