Final answer:
The option that is not a reason for the American victory in the Revolutionary War is the lack of intervention by European powers since, in reality, European support, especially from France, was instrumental in the American success.
Step-by-step explanation:
The question asks us to identify which of the given options is not a reason for the American victory in the Revolutionary War. Based on historical data, we know that the intervention by European powers, particularly the French after the Battle of Saratoga, played a critical role in aiding the American cause.
The support of average citizens was also a factor, as the Revolution succeeded in part due to the unity among colonists from diverse backgrounds in their opposition to Great Britain. Geography also favored the Americans, as they were fighting on their home ground. Therefore, the correct answer is C) No intervention by European powers, as intervention from countries like France was a significant factor in the American victory.