1. The coming together between the Old World and the New World didn't came in the right way at all. The people from the Old World went in to get wealth and they didn't let anything stand on their way in order to achieve that. This included humans as well, and in order to get to what they wanted, the people from the Old World were very aggressive and cruel, destroying whole civilization along the way, which had a lasting effect on the demographic picture of the Americas.
2. Instead of being aggressive and exploit the people from the New World, the people of the Old World should have been focused on cooperation, learning, exchanging experiences, ideas, technologies. This was going to benefit both sides, as both sides had lot to offer to each other. If things were going in this manner, lot of battles and wars would have been avoided, thus lot of people would not have lost their lives, families, homes. The progress would have been much quicker, and the Americas would have developed much better.