This is the story of the Columbian Exchange, the greatest cultural exchange in history. The first part describes the Americas before Columbus. 100 million ‘Indians’ lived in organised communities. One example is the Cahokia tribe, who farmed, built cities and traded across North America. Their land was spacious and provided ample food. In Europe, however, land was increasingly overcrowded, overfished and polluted. It was the American continent’s natural resources that ensured Europe’s survival.