To whom...,
The "fact" (really an estimate) that there were fifteen million indigenous people before Columbus compared with the numbers reported in 1890 does not, on its own, indicate genocide on a massive. Obviously there was both war and genocide against native people, but it is entirely likely that disease was the main cause of native deaths. Influenza epidemics regularly killed ten percent of stricken populations, smallpox was in the thirty percent range, plague as high as forty percent. Add to that the "childhood" diseases and a population could easily be reduced to ten or twenty percent of its original size and very quickly.
If we postulate that the European diseases were originally spread in the new world largely through native-to-native contact (and they had centuries to spread), Europeans encountering the native people after they had been exposed years earlier would not see a calamity of epidemic, since the natural process of sharing immunity would have taken hold. They would, however, be encountering populations that had already been slaughtered wholesale by disease. This would account for a European ignorance of the magnitude of epidemic suffered by native people. Interestingly, within a single generation many childhood diseases are dramatically reduced as surviving mothers help children to acquire immunity while breast-feeding. What happens is that the children actually get the disease but do not suffer its fatal virulence (because they have their mother's antibodies in their system), affording them lifelong immunity. An interruption in this process of children acquiring immunity is what caused the polio epidemics earlier in this century. In countries where breast-feeding children were routinely exposed to the polio virus, polio epidemics were very rare.
peace