Final answer:
France was the great rival to British power in North America in the 18th century, engaging in conflicts such as the French and Indian War. The Treaty of Paris in 1763 marked the end of the war and the loss of French North American possessions.
Step-by-step explanation:
The great rival to British power in North America in the 18th century was France. The British and French engaged in a series of conflicts, including the French and Indian War (1754-1763), in which they fought for control of eastern North America. It was not until the Treaty of Paris in 1763 that France lost its North American possessions, solidifying British power in the region.