Answer:
The factor that contributed to the death of indigenous tribes in the Americas after the Columbian Exchange is epidemics brought by European settlers. The introduction of new diseases such as smallpox, measles, and influenza to which indigenous people had no immunity caused devastating epidemics, wiping out entire communities and contributing to a drastic decline in the indigenous population. The other options, including new foods brought to the New World and Spanish conquest in search of gold, certainly had significant impacts on the Americas but did not directly cause the death of indigenous tribes.