Final answer:
Option C: 'The natives could easily defeat European attacks' is NOT a reason for the failure of European enslavement of Native Americans since they could seldom defeat European military might. Native Americans suffered severely from European diseases due to a lack of immunity.
Step-by-step explanation:
The option that IS NOT a reason why the European enslavement of Native Americans was not successful is C. The natives could easily defeat European attacks. While Native Americans were indeed knowledgeable about the land and could escape, and while there was a population decline due to European diseases, they generally could not easily defeat European military might. On the contrary, they often formed alliances to resist European encroachment, but these seldom resulted in outright military defeats for Europeans who had superior weaponry and military organization.
Concerning the devastating impact of European diseases on Native Americans, the correct answer is C. Native Americans had no immunity to European diseases. Europeans brought pathogens like smallpox and measles to the Americas. Native Americans had no prior exposure to these diseases, which meant they had not developed any natural immunities, leading to catastrophic death tolls and severely weakening their societies. The rapid decline in population due to disease drastically reduced the indigenous people's ability to resist European invaders.