I was always quite hasey on this. I was told many Naitive Americans died off once Europeans made contact with them, due to disease. I do tend to hear a lot of people mentioning that Christopher Columbus was genocidal, but I never actually learned about any accounts of him killing Natives. Did he do these things unprovoked? Was most of these death unwarranted? What mistreatments did Christopher Columbus do to the Natives?
This previous answer by /u/snapshot52 goes over some of the actions carried out by Columbus and the men with him when they arrived in the Americas and discusses the role that disease played.