On the Argentine pampas, between the years 1860 and 1910, a dramatic social and agricultural revolution took place. The haunts of wild cattle, native peoples, and gauchos were transformed into cultivated fields and rich pastures. A land that had produced only scrawny sheep and cattle became one of the world's leading exporters of wheat, corn, beef, mutton, and wool. A country that had had only a sparse and scattered Spanish and mestizo population now boasted a metropolis of one and a half million, and a national population of eight million people, nearly a third of whom were born in...