Answer:
The main damange that the arrival of Columbus caused to the Native American civilizations was the spread of Eurasian diseases like measles or viruela, for which the Native Americans did not have antibodies.
These diseases were very contagious, and quickly spread among the Native populations all over the Americas, from Canada to South America, killing about 90% of the pre-columbian population.
It already is an improper fraction but to make it proper it would would be 15 and 1/2
