1) Population curb: After the Europeans became extremely strong, they forced Indians off their homeland and placed them in reservations and such.
2)Disease: Disease brought by Europeans (i.e. measels, chicken pox, etc)
These impacted the American Indians more than weapons and technology of the days
3) Technology: Technology would be the next. As many Indians gathered and hunt (yes some did farm, not a lot, and with primitive tools), there tool weren't as enhanced as the Europeans (for example, they use wooden plows against the European iron plows. Or they still use wooden spears with hardened points or bows made of wood and arrows with stone points. On the other hand, the Europeans used muskets (IDR if they invented rapid-fire yet or not) body armor (knight's armor type, kinda like conquistadors) and cannons, etc. Technology helped Europeans both gain allies and defeat their enemies relatively easy.
4) Allies and Enemies: As Europeans allied themselves with certain tribes, the other tribes would feel unsafe and the sort, and would make war. This led too numerous wars, and the fall of many Indian tribes (and European powers. Take for example, the French and Indian war).
5) Crops: Europeans introduced many different crops that were later part of Indian food life and the sort. These include wheat, barley, rice, turnips, etc. Some of these crops impacted Indian life, and became one of the many foods they eat.
hope this helps
