Final answer:
Native American tribes merged and governments strengthened due to the need for protection, cooperation, and the influence of European materials.
Step-by-step explanation:
The merging of Native American tribes and the strengthening of their governments were influenced by several factors. One reason was the need for protection and cooperation. Clans joined together to form tribes under a single leader to better protect their herds, households, and engage in united actions like raids on other clans. Additionally, conflicts between tribes increased as more groups were forced westward, leading to the consolidation of power and the strengthening of governments. Finally, the influx of European materials, including weapons, changed traditional power dynamics among tribes and influenced their consolidation. For example, weaker groups gained power against once-dominant groups by acquiring European weapons.